> If that measurement includes questions such as, "Do others find you easy to get along with?" then of course there's going to be a negative correlation with loneliness, because you've essentially defined it that way.

Lack of agreeableness may drive others away, but if disageeable people also want less socialization, they might not be more lonely than agreeable people.

I personal think I'm pretty agreeable, but it would take a lot for me to feel lonely, so even if I were very disagreeable, I imagine I'd still have enough people around to suit me.