Shrug it off. I've been on the Internet since 1985, and IME over the last 10-15 years, the vast majority of Internet forums are dominated by people who want to spread unhappiness. They're probably pretty unhappy themselves. And based on the number of hours they spend posting, they must not have friends or lives outside in the real world. These people should be pitied, because they probably live wretched lives.
OTOH, I don't believe in rewarding wrongdoing. So my advice is to resist the temptation to hit the flame bait, but don't be afraid to state your position in a clear and logical manner. If someone attacks you personally, don't reply to them directly. Instead, speak to the group as a whole. If they cyber-stalk you, just ignore them, no matter what they write.
Everybody's entitled to their opinion. And on privately owned sites they may also have the privilege to act badly. That's life.
I remember when my Mustang was new, and I spent a lot of time on a Mustang BBS. We would get regular attacks from members of a ricer BBS, and before long we got accounts on their BBS and waged our own counter-strikes. It was all in good fun, except for the few who took it (and themselves) too seriously. One good thing that came out of that holy war was that the truly knowledgeable and civil people recognized each-other and became friends. I met the managing editor of a well-known sport compact magazine then, and we had some very productive and entertaining conversations in private.