I dunno, I don't mind. Tl;dr is really an import from reddit, where people often do say long things which don't need to be read to enjoy the flow of the thread. Here, that isn't quite as important, because of the more intellectual nature of the commenting: you really have to read the whole thing to get the whole point. But occasionally, when you just got linked to a really interesting comment, and all you need to know of the post is a broad outline, they can be effective.

But often, tl;drs are good. It forces you to write a short executive summary, which often prompts you to edit the main body of what you've written. It also allows you to indicate your opinions in a slightly more informal way. They're frequently also humourous, which is always good.

So I don't mind them.

tl;dr: tl;dr is not always a bad thing, imho.