I ran one for a while. In Finland legislation is a bit different, so I wasn’t worried about breaking the law or getting sued, but my ISP got in touch pretty quickly. They were professionals and understood the situation when I explained why my traffic might look “a bit” suspicious and I attempted to clean up bad actors from the traffic with filtering and whatnot, but eventually ISP got enough complaints and they were pretty much forced to tell me that either I shut the exit node down or they’ll cut my line.

As I said, they were very professional about it, and managed the whole experiment as good as I ever could have hoped, but my agreement with them has an option that if I’m letting malware and bad actors leave the network even after warnings they can shut the connection down. And that’s understandable, I suppose they have similar agreements with other providers and they received all the abuse mail my exit node was causing, so I’m still a happy customer with them even if they eventually took the hard way.

I’m still pretty sure it would be possible to run filtered exit node, but it would require far more time and other resources that I’m willing to spend on a project like that and I’m not sure if a single person is enough for it anyways.

So, yes, do your homework and be careful. Legislation plays a significant part (depending on where you live), but your ISP most likely won’t like it either.