There are a few different types of blockchain, differing by how they stop you just making up your own alternative chain and saying that is the real history:

• Proof of Work - prove you wasted lots of energy to add to the chain, making it prohibitively expensive to make your fake alternative chain - but also causing lots of emissions / wasting lots of energy.
• Proof of Stake - adding to the chain requires participation of the people with the most total coins in the cryptocurrency already. Essentially 'one dollar, one vote', and 'the rich get richer' brought to crypo.
• Proof of Humanity / Proof of Personhood / Proof of Identity - adding to the chain requires the participation of the most people. Attempts to bring "One person, one vote", and Universal Basic Income to crypto. There are various attempts - some require submission of photos and videos, and have an adjudication scheme built in to detect duplicates (which might fall to AI-generated faces relatively soon). Others (see Worldcoin) require a trusted central party to produce hardware which scans faces and verifies they are real and unique (and have already had data leaks from participants involved in verification). The other option is to trust governments / other existing infrastructure to verify identities (which is probably the most sensible option if you are trying to genuinely just disrupt banking, but many crypto people hate because they also have a cyberpunk fantasy of accelerating crypto-anarchy, and actually want crypto to be used for tax evasion and without the cooperation of governments).

So there are alternatives to environmental impact, but there is currently no perfect crypto. Stack that on top of the number of scammers out there riding the crypto buzz, and it is certainly not that hard to see the reasons behind the hate.

No. No more than, say, Lemmy. It's just a cryptographically verifiable audit log.

This is not aimed at you; you asked a reasonable question. The height of ignorant hypocracy is people complaining about environmental impact (which is resource use) while using streaming movies, music, and online video games. Watching a Youtube video rant about the evils of Bitcoin uses more resources than syncing a day's backlog of the Bitcoin blockchain. Most popular web sites these days are so packed with Javascript, they compete with shitcoin blockchain resource use.

Sounds like you're thinking of proof of work cryptocurrencies. They use blockchains, but are not blockchains themselves. The blockchains part is trivially cheap to compute.