> At least in the US law enforcement can't charge you with anything

Citation please? Last I checked people get charged with things they didn't do, or weren't responsible for, in just about every system of justice - that's why we have courts.

Ah, fair point, I meant convicted. However ISPs threatening to cut off your service for running a Tor relay is a good indication you won't even be charged, as the ISP (and the local authorities) should know you have safe harbor.

This leads to the other issue of your service being cut...

If you want to run an exit node do it on a hosting service. You can get a VPS for $5/m. Why risk getting arrested by running it at home?

Because the hosting service and its IP block are all geographically constrained. This makes correlation attacks easier, as well as attacks requiring physical access.