I fail to see which part of "be kind to animals" is aggressive. It might be inconvenient or annoying, I can even understand how it can be interpreted as rude but aggressive? That is great and it's something kind of inevitable, to talk about your lifestyle when it comes up. How often does that happen online? Do you think that a passive attitude is sufficient to stop cruelty? You do not think that those being abused deserve a more proactive approach? I do realise that it'll be less effective to force people to think about something than waiting for the subject to come up. But what's the option? To just sit back and let discrimination go on unchallenged? We wouldn't do that regarding other types of discrimination, why should we regarding animal discrimination? Should we speak only when we are allowed by those contributing to the problem we're tying to solve?I think you're too aggressive.
I only bring it up when I'm offered food or it becomes extremely relevant, generally when this happens the person(s) I'm speaking with already consider me a friend.