Just because you are intelligent, it doesn't mean that you can'r be stupid. In this case we should criticise the post and not the poster. We criticise the poster when he keeps repeating the stupidity. Now we come to the problem of the assessment of stupidity - I believe that anyone who believes that Britain should stay in the EU is myopic and stupid, but nearly 50% of the UK may not agree with me. So how can we determine the group opinion of stupidity - I think informed discussion is the answer, and I agree the the attack should be on the opinion, and not on the holder.
That works when they are voicing an opinion they believe in, however, when they are clearly demonstrated to be pushing double standards and only voicing an opinion in that specific context to solidify the double standards but then a totally different opinion when it is applied to themselves or their friends- then the attack on the person is clearly warranted.
Debate is the only way to thrash out the optimal opinion. Once you have won the debate and debunked all opposing argument then if they continue to proliferate those debunked views that comes under trolling here.
Even then if people have not first attacked you or used bad language in your direction continuously, then if you can stick to making sure your points are clearly and undeniably dominant and crush their spurious nonsense you may not feel the need to get into a swearing/insults/snide pisstaking banter/not banter with them. Does not really matter to the discerning reader, that will pick out the valid points from the mess regardless if they are REALLY interested in finding out the truth or optimal solution.