I think if someone ASKS, and you give them your honest answer, and they are defensive or rude, I'm really sorry -- you did the best you could. :/ The most you can do is just make a mental note not to bother next time they ask. (As an aside, if they DID NOT ASK, then you really should've asked if they were looking for critique!)
I think there's a place here for discernment, though. If someone says "Hey guys, here's the first chapter, tell me what you think!!!" that might... not actually be asking for critique. That might be someone who wants you to comment if you liked it or if the chapter left you with thoughts and questions -- because so many readers don't think to comment saying "I really liked this!" It NEVER hurts to ask, "hey, when you said you were looking for feedback/opinions/whatever, would critique be helpful or are you not really looking for that right now?"
Another thing to remember is that a lot of artists are not taught that it's okay to not be ready for critique. They think that not seeking critique would make them a bad artist, that they HAVE to. So there will be people who ask, because they think they're supposed to, but they're not ready for it when they hear it. It sucks, and it sucks to get a defensive response when you have taken the time to give someone your careful thoughts, but give a little bit of grace, if you can. :<
The advice I'd give to artists would be different. I would talk to them about handling inevitable harsh comments and how to deal with critique that isn't kind, because it's going to be there. I would tell them you don't have to listen to critique you didn't ask for, but you should still consider it, and it's good to respond politely (even if it's a polite "I'm not looking for critique right now, but thank you!") But I think it's weird to say to an artist "some people are going to be rude, try to deal with that" and to say to a commenter "therefore, be as rude as you want."
If you're frustrated that your critique isn't being taken well, and want to figure out how to change that, then I think the best way would be to save your critique for those who are REALLY seeking critique, and to do your best to learn how to be cautious and discern who's REALLY seeking critique.