To me, this is the crux of the problem. Consent to sex is defense against rape and SHOULD be defense against this law. We can argue of the age of consent but certainly, if an 18 year old can buy a rifle, serve in the military, own a car or a house ..., to me, they can give consent.
A minor, under 18, in my opinion can not give consent.
I agree 18 and over should not be a felony but the employee should be fired. Students are not there for the sexual use of teachers.