So you have no problem with an adult in an authority position grooming a child for sex as long as the adult waits until that child turns 18 to fuck them? To you it's like taking a kid on several dates or extended foreplay until the clock strikes twelve then they become fair game.
You should become a foster parent. Raise your own potential sex partners.
This is a separate crime entirely. It's illegal to try and coerce a minor into sex, which is what you're describing, even if you tell them it can wait until their 18th birthday.
It's not illegal to hit on an adult in most situations unless they tell you to stop at which point it becomes harassment.
Can you explain to me who this law is bigoted against? That is not clear to me.
I also don't understand why you are hammering home the point that they are consenting adults. The issue is not their age, but the nature of their relationship. I think that there's a reasonable case to be made that, regardless of age of consent, the state has a compelling interest in discouraging relationships between students and teachers. It oughtn't be particularly difficult to wait 9 months until the student has graduated in order to begin a sexual relationship with him or her.
I agree that 20 years is overmuch, but I also don't think that's what we should be expecting her to get.
There's a huge difference between discouraging such relationships and outlawing them. I'm adult, I should be allowed to have sex with another adult if they consent. Even if that person happens to be my teacher/college professor/boss/whatever. The government should not be able to arrest the person I had sex with when I wanted it in the first place. That's just nuts. I find this law bigoted because it's essentially giving the government the ability to decide who can and can't be in a relationship.
If the government can arrest any "sexual deviant" they want, well we already know the results of that from history.