If those people have the time to come on an internet forum, they have the time to read whatever post they come across. If you don't have the time to do that, don't spend your precious few minutes online.
Especially if you're going to take the time to post "tl;dr."
It's a different story if the OP is just poorly formatted/written, but if it's just long, and it's a topic that interest you and the length is the only thing that's stopping you from reading it, then you should just read it or leave right away.