"Why should the punishment be equal (or comperable) when the violation is of a different nature?"
Exactly. So logically I would assume you believe in the counter argument, that if the violation is of the same nature, then the punishment should be the same? Here we are talking about a violation that is the same. A man does it, he gets jail, a woman does it she gets a pass..
This is the only difference. (we'll proffer that on a case by case basis details may vary, of course, but you get the point)
The violation is clearly not the same. THAT's the point.