I'd be opening up a can of worms that I'm not sure I have the mental energy to organize, source, and talk about in length right now. I will say that if you've found a tolerant and science-accepting vegan group, that's super awesome and honestly not as common as it should be.

Here's a few veeeery summarized points:

1. Humans are not made for veganism. It can be dangerous and make you very sick, so you need a lot of education on nutrition and a lot of non-natural dietary supplements to make it work. Because of this, forcing veganism on children is also considered child abuse by law in some countries. Either way, you should always talk to your doctor.
2. Healthy veganism is a privileged diet. The logistics for growing, transporting, and preserving food for a vegan diet balanced enough to not get sick is a big deal, and everything gets expensive and out-of-reach for many. If veganism isn't an option for everyone, non-vegan practices will always be a thing. In which case, vegans shouldn't be snobs towards non-vegans.
3. Grazing animals are actually very important to healthy soil and crops. And that means controlling where they graze. And at that point, you're going against what a lot of vegans stand for. And honestly, at that point just use the animals for meat, too.
4. Vegans often condone practices that are unhealthy to humans or animals, and that kill off a lot of animals in order to sustain their agriculture. Not to mention the absolute need for pesticides to sustain large populations, and pesticides can kill off a lot of things on their own. Veganism is (usually) about not harming animals, but agriculture always kills a lot of animals; so one like myself will argue why many vegans are such snobs towards non-vegans, as if veganism is more "pure" than non-veganism