I always try to make a special effort to review a story postively if it has any stupidly negative reviews, and make a comment to that effect.

I think that, within reason, reviewing a story based on its content is appropriate - meaning that if something is really repulsive to you, and you weren't tipped off that it would be that way because of the codes/synopsis, then it's fair enough to complain. If, on the other hand, the code said 'M/m', and you don't like Malesub stories, then giving it a bad review makes you look like a jerk.