Perhaps, but it depends on the customer. A crackhead who wants a gat probably won't even know what ammo to load in it. (Apparently it's somewhat common for police to arrest street criminals with a gun loaded full of the wrong caliber ammunition). And unless you seriously overpack the round or make the barrel out of pot metal, more likely the quality problem that you will get is the gun failing to fire or failing to cycle. Remember though, you are talking about criminals, not people like you and me who care about safety ratings.

Therefore, we should acknowledge reality and form policy around that rather than pissing into the wind while pretending we're doing something useful.

For example- if you want to attack the lion's share of gun violence, address the causes of it, rather than the tools used in it. That means address drugs and drug gangs. Decriminalize or legalize drugs, put the gangs and cartels out of business. Treat addicts like patients who need help rather than criminals who need punishment, or at the very least stop locking up non-violent drug users with violent criminals (and thus turning them into violent drug users).
Let's also tackle poverty. Poverty is strongly correlated with drug use, so let's give people some hope and upward mobility so they don't feel desperate enough to use drugs. Doesn't work for everybody, but a good intervention that takes a young kid from the hood and gives him opportunity and resources so he has an obvious path to make something of his life will keep an awful lot of kids out of gangs and drugs.

Of course these solutions require more work and money than passing another law that criminals will ignore and getting your photo taken and saying I Did Something!.

Okay so full answer from a real keyboard. Please consider this one to supercede the last one which was written on my phone on my way to sleep.

First- addressing your argument:

I argue there ARE NOT would-be bombers out there saying 'I really wanna blow some people up but I can't get explosives, my reign of terror ended before it began :(, curse you explosives licensing schemes! Guess I have no choice but to get a job and therapy.'. Evil men will always find the tools they need to dispense their evil.

But there's a sliding scale. The more determined someone is, the more stringent restrictions it will take to stop them from getting whatever they want. There's a limit to what's practical, and a higher limit to what's possible. Look at prisons- the most secure, controlled, patrolled environment in the world, and yet prisoners still get drugs and weapons and cell phones. Evil men will always find the tools they need to dispense their evil, but assholes are more likely to settle for whatever's convenient.

So by 'if 7-11 started selling dynamite', that means drop the difficulty of acquisition to zero. And in that sense, of course there'd be more bombings- both because 'Dynamite sale! 12 sticks for $12' posters in the window would bring bombs closer to peoples consciousness, and because you now cover the entire scale of determination.

Second, my argument:

Bombs are a bad analogue because you can't use a bomb defensively. If someone threatens to bomb my car, having my own bomb won't help me much. And a bomb isn't directed, it's broad destruction that harms everything in its vicinity (buildings, people, vehicles, etc). So I can't use a bomb to defend my home from an intruder as I'll just blow up my own house & family; I can't use a bomb to defend against street crime because I'd blow myself up too.

A gun however CAN be used defensively. It doesn't harm everything in the vicinity, just whatever you shoot at. The gun doesn't also harm the shooter, doesn't also harm everybody nearby. I can shoot the intruder or street criminal without also harming myself or my family.

So consider Night City, or any similar society where you can assume everyone you meet is armed. In that society, much like in ours, you have two classes of people. There's the criminal class- which includes the main character V. They go about their illegal actions, using violence against anyone who stands in their way. And there's the average people. In a game like CP2077 or GTA, the average people are the NPCs that populate the city but with whom you have little or no interaction other than stealing their cars or wishing they'd get out of your way.
Obviously we'd like to disarm the criminals. But as people who don't follow the law, that's easier said than done.

When in the beginning of the game you hear the news report that there were 87 murders last week, notice that it's talking about gangs and cartels, not innocent bystanders? Art imitates life.

But now consider the NPCs. Imagine if every time you had to steal a car, the owner would try and shoot you, and if you shoot back then random bystanders would shoot you. Would that impact your willingness to steal cars? I think it would, you'd go looking for parked cars to avoid firefights.

And that's why I say having a mostly armed society is not an awful thing.

I think you do me an injustice, and needlessly so.

The US is not 'just one country' with the same ideals and attitudes everywhere. We are 50 states, and while there is an overall American culture, each state or even city area has its own local culture, ideals, politics, etc.
I live in a 'blue state' (IE Democrat-majority, Democrats are generally an anti-gun party). There's not a big gun culture here. There are not people with 10 gallon hats and a 6-shooter on their hip riding around in a giant pickup truck with a gun rack. My state has more gun control laws than most in the union.
When I grew up we had no guns or interest in guns. During my whole childhood the only exposure to guns I had was once at summer camp there was an activity shooting .22LR rifles (small caliber), lying down, at targets. And once on vacation we went to a shooting range that was part of a resort.

If we'd had this conversation 10 or 12 years ago, I'd have been mostly on your side. I recognized the 2nd Amendment was a thing that existed, but I saw no reason anybody needed an 'assault rifle', I thought gun free zones were a pretty good way to improve safety, and overall a lot of 'gun culture' seemed like needless penis extension.

It was actually one conversation that kicked off a change in my position. An old friend of mine and I were getting lunch together. This guy has always been very Republican (pro-gun/conservative party), owns several guns, goes hunting, etc- but we have a lot of mutual respect despite differing worldviews on many subjects. Anyway, as we finished lunch he mentions that he's going to buy an AR-15 rifle and would I like to come along? I made a dumb joke like 'damn man, I didn't realize it was that small, I'm sorry dude'. He just laughed and said 'You know my deer hunting rifle, the one you said you have no problem with civilians owning? Well it's actually a lot MORE powerful than an AR-15.' I started to argue but he said 'look, nothing I say is going to convince you. So just Google it when you get home, okay?'.
I KNEW he was wrong- a 'military weapon of war' would definitely be more powerful than a stupid wood stock hunting rifle like Elmer Fudd would carry. Surely the military wouldn't be carrying weapons inferior to those of random civilian hunters, right?

So I went home and Googled it. And I found he was right- his .30-06 hunting rifle has SIGNIFICANTLY more muzzle energy than the .223 AR-15 he was planning to buy. The hunting rifle was larger and heavier and in almost every way, more powerful.
I'm usually not wrong about technical things. So I was curious what else I was wrong about on the subject, turned out it was a lot. Not about policy or position, but about provable technical things of how guns work and how deadly they are and whatnot.
So I decided the best course of action was to basically forget everything I thought I knew, and start fresh. That kicked off a good 3-4 week deep dive on the subject, reading articles, watching YouTubes, doing research on both sides of the issue.

This brought about a few basic conclusions. The biggest is that most of the politicians who talk about guns appear to know little or nothing about guns, as many of their gun control arguments are easily disproved on basis of fact. And many of the laws they promote do nothing to regulate the actual lethality of guns, but rather try to describe 'scary looking guns' and ban those. For example, my own state's laws regulate rifles that have ergonomic features like a pistol grip or collapsible stock that have NO bearing on the rifle's lethality.

I then started doing research into use of force, defensive situations, etc. And that brought a very sobering realization- I lived in a bubble. Violence is not a part of my life (and I prefer it that way). My area is quite safe. But that doesn't mean I am immune to violent people- and there ARE people out there who ARE violent. Not many near me, but they exist.
And I'd say I've done more research than most into what happens in a fight. I've seen a lot of videos of defensive situations- robberies, fistfights, assaults, kidnapping, and straight up attempted murder. I've seen what happens when people get shot (you won't find it on YouTube). And I've seen how easy it is to seriously harm a human. We live safe lives in civilized society, but on the scale of the world, our bodies are pretty fragile and it doesn't take much to seriously damage them.

And that's why I say thought experiment for how to kill someone from 100' away. It's why I say that if someone wants to kill people, they will, gun or not. It's why I reject the logic that removing guns will save lives, because I recognize that gun regulations affect the law-abiding more than the criminals who are doing the most harm.

Point is-- I have done the thought experiment, a few different ways.

Do I want guns in vending machines? No. Is the absolute ideal to have everybody armed? No, the ideal is where nobody needs to be armed. But absent that perfect future, I think civilian armament as a deterrence to criminals works.