As long as p2p exit nodes are relatively uncommon, it will be relatively unbelievable for you to claim that "someone else" was doing the illegal things on your network.
But if p2p exit nodes were orders of magnitude more common, then the burden of proof would indisputably be the responsibility of the prosecutors, since anyone could credibly claim "someone else did it."
And that's why this trope of "but what if someone does bad stuff on your network?!" is so frustratingly self-defeating: if everyone just ignored that risk, then everyone could have a p2p exit node, and the risk would be mitigated. It's a sort of prisoner's dilemma where nobody wants to be the early adopter of a system that would, on the whole, benefit all of us.
A society is difficult to surveil when everyone uses Tor as both a client and an exit node, and onion routing is the default method of exchanging packets (some might say it should have been incorporated into the original design of the internet). So it's perhaps worth noting that adversaries of society, such as the NSA or FBI, have a great incentive to perpetuate fearmongering about p2p networks and the threat of "but whatabout muh criminals on muh network!"
If you're reading this, maybe it's time to setup a Tor relay (with config flag `ExitRelay 1`).