I buy doujinshi for the art.
First, I would be missing out on worlds of good stuff if I was limited to what I could read.
Second, I'm sure there are plenty of good ero fanfics out there but I'd rather not read them, because there is no art.
Third, its better to make up your own story, well not always and sometimes I wonder - but theres plenty of times where what I had in mind was definitely better - like when I thought that was a chick.
Fourth, a lot of doujinshi artists seem to put the art first and story second. Hmm I wonder why, it must have something to do with my preference for art.
Fifth, ?? profit etc.
but you can't change people, rather they'll change themselves over time. Unless they have better things to do like play halo 3.
as long as people who like doujin don't segregate, you see bad works by good works but some people like art but have a thing for crappy looking sketches that fit their fantasy of a nice girl and some people just snatch up every akiko minase related book thats graced the kbooks down the street. but its all good.