Instead, what I encounter more often is if I don't immediately agree with someone they say, "we have to agree to disagree." Which is no agreement at all. It's shutting down communication and preventing me from understanding why we disagree. I learn nothing from people who say that to me and find it frustrating.
Have you ever heard someone arguing "Reason is on their side"?
Skepticism doesn't entail blocking out viewpoints you disagree with. You automatically lose an argument if you refuse to engage with your detractor.
Nah. If someone who believes the Earth is flat is willing to spend 12 hours a day arguing on forums, your best move is to refuse to engage. You will never convince them, and they will always outlast you and feel victorious.
I have had experience elsewhere with someone who trolls various forums in an effort to spread the "good word" about Jehova. Sometimes, "The only winning move is not to play." It's not always the case, and sure, that line can be used as an excuse by people in bad faith to avoid an argument; it's still the prudent course sometimes.
Trolls are there, all over the place, but there are "True Believers" too, and they're even more immovable and pointless.
The issue is not that people make a serious and earnest effort to understand the opposing side, but tire before they're able to understand the other POV. The issue is rather that they apply one or more of a handful of ethereal, unfalsifiable labels to their opponent, and then believe that gives them license to dismiss the opponent's POV out of hand without addressing or processing it.
When such people hear something challenging to their favored notions, instead of saying "Wow, I'll need to think about that", they say "You're a [bigot|racist|%phobe|redneck|yuppie|commie|socialist|...].", mutter additional insults under their breath, tell you not to try to show your disgusting ignorant face around here anymore or else, and pat themselves on the back for their righteousness while they walk away.
Also most of those labels are falsifiable.
You just described the battle cry of the eternal troll. Your freedom of speech does not equal me being forced to listen to you.