I get it - had to deal with a similar situation. This guy kept adding me to chats, and whenever I left, he'd get offended or catch me on some supposed injustice. Here's the thing: later I found out he did this with a bunch of people, and most of them just quietly left or stayed silent in those chats without saying anything. So it's his habit, not your problem 😐
The word "snob" here works like a noose, basically. Your friend is guilt-tripping you into staying and proving you're a good person. But a normal person, when they hear "I'm not comfortable with this," just accepts it. They don't try to prove you wrong. If he thinks it's normal to call your personal boundaries snobbery - that's about how he treats you, not about reality.
Practically speaking: text him once, keep it short. Don't apologize, don't argue your case. "I appreciate you trying to include me, but group chats with strangers don't work for me. I'll be leaving them." Done. If he starts playing on your emotions or accusing you again - just don't respond to it. You don't need to convince him you're not a snob. The other answers are right: this is manipulation, and it only works if you play the game of "prove you're good." Don't play.