I think you are overlooking the romantic side of these relationships.
What makes these relationships even more disturbing in my opinion is the fact many of these female teachers claim to be in love with the male students and want to marry them when they get out of jail and the students are the legal age to do so. Some people believe they form a Mother’s love for them to begin with and the closer they get to them the more that love evolves into something else and the same can be said in some cases with male teacher/ female student relationships. I just think it is sick and twisted and the gender of the offender doesn’t make a difference to me. As for people believing all women are pure and innocent I don’t think anybody believes that except maybe Dave up the road and Dave up the road isn’t the sharpest tool in the shed. My Wife was severely bullied growing up by boys and girls and the girls that bullied her were far from ‘pure’ or ‘innocent’ as you put it. There are good and bad women in the world just like there are good men and bad men and gender has nothing to do with it.