There's another important difference. Dating inside the dojo is one thing. A teacher dating a student is another, not unheard of, something you look at askance, not to be encouraged. But just propositioning your student? Nope. That's pure predatory behavior making maximum use of the power imbalance to use her like a cut-rate whore. And doing again after he'd been turned down? The guy is scum, and anyone who'd defend or even tolerate him is scum.