He has an opinion, like any other poster, and has the right to voice it, even if it is unnecessarily rude or snarky. How you choose to react to it is more important IMHO. You can certainly defend your position - he's only one poster on the very, very, very big internet, after all.

I would suggest you read all the responses you get, even from people voicing disagreement, and then learn what you can - it's often disagreement that enables you to sharpen your argument to a better point.