[Note: here's the post about Jon Henke and The Next Right.]
As you can see below, dozens of sites have deleted my comments over the years, or they've moderated them away, or they've gone as far as banning me. Reviewing the comments in the entries below will show a pattern: they were on-topic, they weren't abusive, and they pointed out how the author of the post was wrong. When an author deletes one of my comments, it's almost always the case that they're admitting the weakness of their arguments and they don't want their other readers to find out how they're wrong.
When a site deletes (or moderates away) valid comments, they're more than just an echo chamber. Because of their policies, nothing you read at that site can be trusted. You have to check every single thing they say because they've disabled fact-checking. You never know what was deleted, and it might have been a comment that pointed out how they were wrong.
The most egregious case of this was RedState. In 2006, after almost a year and a half of posting entries - not just comments - at that site, I was banned. I have yet to receive any reasonable explanation, and the closest they can to providing me one was based on their misreading of my last entry there.
On the other hand, Washington Monthly deletes comments so quickly and so reliably that it's almost a joke. Note that they've deleted comments without links or just with links to Ann Althouse and National Review. They're very eager to make sure that their readers don't find out how they're wrong.