That's what I thought at first too, but I finally got to one point with one person where I couldn't keep myself from responding to their (what I felt was) trolling. I thought it might be temporary, just until I recalibrate my expectations, but I found that on the occasions where I show their posts I don't feel I've missed anything useful, and I still get very, very annoyed by some of their comments, so I've left it in.
The only problem is that they've started a few threads that I do find interesting, so I have to go to a little extra effort to participate in them, but that's a small price to pay for keeping an even keel.
In short: I'm ignoring someone due to my own weakness and inability to let some things go.