It's an interesting piece of advice.
It strikes me that when dealing with someone who has a mental/emotional/social problem that's radiating out into a group of people, people proposing solutions and saying how everyone should deal with it often make the assumption that
everyone else in the group has excellent mental health
and in fact are all wired the same.
But I think that's rarely ever true. Probably never. If you experience something as annoying or not a big deal, someone else may experience it as very aggravating, infuriating, something they aren't able to ignore. They may have their own issues that complicate their reactions and their ability (or lack thereof) to allow the events to fall away from them and stop creating stress/upset/anger/etc.
Some people may not be able to ignore it. Some people may be able to but at the cost of a colossal amount of effort that they can't afford to budget into their allotment of mental/emotional energy. We're all so very different.
And I agree, some people can be mean in a way that seems recreational. I don't like to see that either, especially if the person being insulted probably isn't going to understand the joke. But I also feel strongly that the people reacting have a right to their own reactions, which may well be different from yours.
We're a whole group of people each with our own problems and failings and sensitivities and needs, and when an experience reaches a bunch of us, we'll each process it in the way that we do/can, bringing all that we are (and are not) to those interactions. Sometimes there's going to be trouble. Just the nature of the beast.
Mark has alot going on, and he has the right to exist. (That right has limitations, as he's finding, getting some members' reactions to his massive posting frequency coupled with some of his content/style.) But the rest of us do too. We have stuff going on, and that affects how we react, how we're able to react/not react, and as such, we have the right to exist too.
And just telling people to "ignore it" is awfully disrespectful of that.