tha doesnt really encourage more crime. if you allow for your dilution theory, more people would gang rape, in exponentially larger groups, so that each would be barely punished. Your logic is stupid
The punishment is still significant enough that even with a large group, they could spend at least a few months in jail. And this system is completely fair, I don't see what the problem is. For example, if 100 people stole $100,000 from a bank, then they would be expected to each pay $1000 back to the bank. That's just the way it works and it's the only fair way to do it imo.
Besides, if 1000 people all "raped" one person, I bet most of the people would all just be standing around doing nothing. There's only so many people that can rape someone at a time. And if the rape lasts for hours, then extra jail time should be added to take that into account, so that even with the "dilution" as you call it, they will still end up with a significant jail sentence each.