I think it makes sense to only comment on a school if you have experience of it, but it can help people to hear the negatives awell. However, i do not agree to slandering the schools, mainly put it across as a point of view or experience. This can include people who have visited, but decided not to go there.
I beleive that these comments can be just as helpful as positive comments, provided they are under control.
I'm not disagreeing with the above post, i just thought i would add that to itt, if you don't mind