At least 80% of the groups on LFG are full of trash people, either by skill level or personality.

This is pretty much true -- I mean, people who have good personalities and/or skill levels general don't have too difficult a time finding people to play with on a regular basis. People stuck in the LFG grind are there generally because A) they are just starting out in the game B) they don't have enough time to play to form social bonds with other player or C) they are terrible and/or annoying.

But this is why when you find that 20% of non-trash LFG players you should go out of your way to befriend them and get yourself out of the LFG hell.