In such cases if it is not your topic, if you are not the OP, there is no compulsion for you to respond. If however you feel you strongly disagree or have information that you want to pass on in a friendly spirit, since you see that the OP is mistaken, then you can give a reply.
It is up to the OP to take in the spirit it was offered. Often the people who reply take it upon themselves correcting all wrongs. Then it becomes a had banging contest.
Once the OP begins insulting, there is no need to interact with him/her at all, whatsoever.
But to pin everything on the OP is naive. One has to admit in all honesty that people do get a certain pleasure in going head to head in verbal jousting. It takes two to play. There is definitely some enjoyment on the part of the posters to uncover the truth, to prove the other guys wrong.
Some people just post rubbish...almost all threads get overun by a just one or two people who just keep posting the same things, and going at each other. Nobody else gets a chance. It's insane.
The OP should have the right to block and delete. This is a chess forum commuity. We are here to have friendly discussions.
This is not a forum for finding the cure for cancer or unearthing some great truth. Deleting stupid posts won't spell the end of the world.
People really really really gotta learn about boundaries.
What about if the OP himself is the author of such rubbish ?
You've not been around at the glorious times of Master_Valek, I guess. This guy had posted 3 threads/day in his two years here on the site, one of which "asked" for opinions about the "gambit" 1.Nc3 e5 2.b4 ?. He then proceeded to defend his opinion against those of higher-rated players, insulting and quoting them out of context, etc.