Opinion: I'm not against veganism, only 'internet veganism' that online spaces create
I know why many vegan people may get upset when you frame it as a cult (and no, hivemind, animal sacrifice isn't a thing in all cults, the opposite), because framing a lifestyle and ethical choice as a cult isn't fair.
The fact is that, even thought you won't admit it, the internet and social media made it so easy to create cultish spaces, so that extremistic ideas vegans show on internet (from Disney - esque ideas about animals, forcing carnivorous animals to become vegan, thought it isn't healthy for them, even ideologies that frame any domesticated animal as a slave) have more ways to spread.
Online spaces often create echo chambers that dictate what one from that group has and cannot do. Reddit, for example, just makes echo chambers an easy phenomenon, so the "us vs them" mentality gets way stronger, alongside the cultish behaviours (and cults now spread even thanks to social media)
This isn't just about veganism, as even media fanbases act too often like this, creating a toxic environment.