I was gonna say something quippy myself, but, then, for some totally unexplained reason I found myself very, very hungry… 
The best thing to do is to write a long dissertation of caveats, save it in a text file, and then append it to the beginning of every post.
“To begin with, yes, I’ve stopped beating my wife…”
It’s good if your wife has a blog so you can provide a cite.
Gawd, I hate that.
Post: “I disagree with my Congressman, who is pro-life.”
Bullshit Response: “Single-issue voters like you make me sick. You don’t care about black lives, or the environment, or Chinese dictatorship, just only your one single oh-so-holy grail of abortion rights.”Mega-huh? That wasn’t what was said at all! And, damn, it sure happens here a LOT.
What’s even more common and can be even more frustrating in its subtlety is when debate opponents don’t explicitly assert incorrectly “you’ve said X”, but simply treat your argument as if you had and respond accordingly, sometimes at great length. For example, suppose one poster points out some flaws with a particular highly touted climate change model, and another poster’s response is focused on forcefully defending the general concept of global warming and attacking denialists. The first poster has two options, neither of them appealing; either ignore it and look like a climate change denialist who has no response to this guy’s attack, or point out that he did not deny climate change etc., and end up not only put on the defensive but having the entire original point completely sidetracked and obscured.
As above, this is extremely common and is a huge problem. (FTR, I don’t think there’s anything the moderators can or should do about this.)
Just thought I’d point out that it ain’t just the Pit. I’ve run into this even more in Great Debates and Politics.
And you just have to “Let it go / let it go…”
Agreed. But due to the prevalence of this tactic, the “it” that you have to let go of might include “engaging in serious discussions on this MB …”
Wasn’t there a Nazi Doper who got banned from the Straight Dope a few years ago - without even a warning - for refusing to reply to posts directed at him in the Pit?