Why you can't stop 'abuse' of file sharing services
I hope that everyone will agree that filtering 'banned' content (whatever that is in your local jurisdiction) is in practice impossible. Users are happy to rename files and otherwise obscure them in order to evade machine inspection, and no one can afford to hand audit everything that is being shared.
(Arguing that people must hand audit things anyways basically amounts to arguing that no one can run a file sharing service.)
This means that the only thing you can really do to deter this banned content is to make your service 'too unattractive' for it. But because you can't tell good content from banned content, this means making your service too unattractive for sharing things freely in general, and this means dooming your service to at best obscurity and at worse complete failure (regardless of whether it is commercial or just some free software that you want to see widely used). This is not exactly an attractive proposition, to put it one way.
(There are all sorts of ways to make your service unattractive; restricting what sorts of content you'll accept, making it awkward to upload or download, insisting on detailed registration for people who want to upload stuff so that you can trace 'abusers' precisely, and so on.)
(Demanding that people take steps to deter sharing of banned content anyways is tantamount to demanding that new file sharing services cripple themselves right from the start, right when they most need to get people interested.)
The inevitable result is that every file sharing service that is actually useful has and will always have 'banned' content; the more useful the service is, the more banned content it will have. The only way to have no banned content is to have an all but useless service, or one that is extremely restricted in scope.