Evilish's counter argument to this was that it was basically the same as Trakata (turning off your saber mid-battle to throw off opponents), but
1. Sith only banned Trakata because they viewed it as cowardly, not unfair. They have no reason not to dick slash.
2. Trakata shouldn't even work, realistically, unless you are actively trying to hit your opponent's blade instead of their body. It's a stupid tactic.
3. Sith are supposed to do whatever they can to win a fight, be it tripping the opponent, force pushing them into buzz saws, anything (that they don't consider overly cowardly). Dick slashing should fall under that.
Albeit, dick slashing is less effective against female Jedi, but that's not much of a reason to not do it against an enemy.