Let's not forget that profic is more like fanfic than is often claimed.

You are so right. Much genre fic certainly builds on established conventions, like the romance novel set on a ranch.

There are so many damn fine fanwriters who know so much about how people behave and how language behaves and can convey it all that it makes me angry, or at least disappointed, to see readers and writers condescending to each other.

This I completely agree with. Some of the fanfic I've read could compete any day against the literature I teach to my students. Some of my favorite writers, period, are fanfic writers and not profic ones. There's brilliant writing and poor writing on both sides of the fence.