Is it? Legality aside, if you define the limits of unacceptable behaviour then you're also saying that anything outside that is acceptable. If you hire decent human beings, hopefully your team can use their judgement and empathy to tell whether something's OK or not, rather than "S/he shouldn't have been offended, I wasn't breaching the rules laid down in the HR handbook! Grow a pair!"
(On the flipside, if you hire decent human beings then nobody's going to be looking in the HR handbook to determine how far they can push harassment without being fired anyway.)
I'm sure that there are decent human beings that fall into these kinds of relationships. But when you want to avoid situations like this Tinder situation, and you actually want to do something about it in advance, rules are things you can point to in order to change a situation. You're waiting for shit to hit the fan when you assume the best of everyone.
