I host a PeerTube instance for my choir and I don't quite care about the existence of PeerTube instances hosting questionable content. I didn't enable federation though. Still hesitant to do this.
Maybe the current system works after all? Just don't visit those instances you dislike, this is what I do. Give people the option to choose for themselves whether they want to partake of material which you or I or my neighbour or his dog finds offending.
Imagine using WordPress to construct your website. If some page existed that listed all the sites that use WordPress, and that listed some disagreeable ones (as it surely would), that has very little impact on your usage of the software.
So, no. Either everyone is censored or no-one is. I vote for the latter, let the law decide what is allowed and keep it at that. If it isn't forbidden, it is allowed.
[1] this is not a joke, see https://www.vox.com/the-goods/2019/2/25/18234950/knitting-ra... where they seriously talk about 'Fiber artists of color' (?) pointing out the 'racism' (?) in the knitting 'community'.