Since I've seen this come up before in many previous discussions of Tor I think it's worth emphasizing/clarifying up front: Tor relays are not the same as Tor exit nodes. Relays do not talk to the public internet, they serve only the full encrypted internal Tor virtual network. So they won't ever send out traffic from an IP under your control to some website or general Internet system (and in turn tie that IP in any way to spam/abuse/whatever, at least not for that reason). It's not necessarily hidden that it is acting as a relay, but the relay itself will have no knowledge of the traffic it's carrying.
Plenty of people have reasonable concerns about the risks/inconveniences that might come with acting as an exit node, but on both a legal and practical level there are many more jurisdictions where merely relaying encrypted traffic between other relays isn't a problem. And it's still quite helpful, both for network speed and because purely internal Tor Hidden Services do not need any exit nodes at all.