No one is going to engage in a serious debate with you when you look prepared for an academic beat down.

If someone attacks your work in a nasty way, don't get angry. Say instead something like:  “it’s interesting that you should say that because my research (cite some book or blog post) seems to suggest that the opposite is actually true. Is there some study or paper you can point me to that would validate your claim?”

Make it your critic's job to prove themselves to you, rather than the other way around. 

99% of critics disappear when confronted with any kind of rigorous intellectual challenge.