Anyone who says 'It's not like it was rape' or 'At least he didn't rape her' is basically admitting that they think it's totally fine for a man to masturbate in front of women in a situation where the women don't want him to.

I wouldn't bother debating the issue because they don't believe that women can be hurt other than physically hurt, but insisting that they condone the behaviour might make them think. Or at least shut them up.