I think it should be rare that a guest of yours spontaneously decides to beat you up without generating any other evidence. So I think we can wiggle out of having to totally solve this problem by emphasizing:
> Maybe we should not lock up *very many people* for whom there isn’t any hard evidence of their guilt.
This should be very rare, so even if we caught everybody who spontaneously beat up their hosts, there still wouldn’t be very many people in this category.
This doesn’t mean we don’t have to investigate any crimes of course. It is important for the legal system to work for victims too. But if you get beat up and point to some guest of yours, an investigation can start, a search warrant can be generated, we can see if they’ve discussed it with anybody, etc etc.