Check out this post, but its better for the health of the network for there to be a diversity of exit node providers, so its better for folks to run one themselves, especially if they are in an under-represented country, or not in the cloud etc.
I support the Tor project but I have to admit that I am far too much of a coward to run an exit node on any network associated with me.
I know most usage of Tor isn’t illegal, but I don’t think it’s much of a secret that there is a fair amount of illegal stuff available on Tor, and I don’t want the FBI knocking on my door because my IP has been tied to some kind of kiddie porn site.
You don't have to run an exit. A middle node is as important as an exit. And running a non-exit relay is pretty hassle free. You will get blocked by some sites, especially banks and governments unfortunately so be aware of that if you want to run one at home. There is a list for ISPs that allow Tor nodes [0] but diversity is important so if you know an ISP with generous traffic allotments that's better. Just check the TOS that they don't explicitly forbid running a relay. Or you could run a bridge to help censored users connect to Tor.
There is also some information on the community site about running and setting up all kinds of relays or bridges [1]
Having run an exit node for a couple of years, the worst part for me was the spam associated with torrent traffic. I got several notices per week of copyright requests, which I responded to with a form letter fuck off, but it was still obnoxious because my upstream required me to do so, creating a ticket that they would not close until I had responded.
As far as dark websites, you are supporting them whenever you create any node, because any node can act as a hop for onion sites. On the balance, I think that it is worth having anonymity through Tor, but I will admit that that balance often seems a razor's edge.
In this particular case, it's not about supporting them, so much as I am just scared of being questioned by the FBI or something, or having my bandwidth throttled because people are stealing porn or movies.
I might still run a middle node at some point, because I do support Tor and want to help.
I know most usage of Tor isn’t illegal, but I don’t think it’s much of a secret that there is a fair amount of illegal stuff available on Tor, and I don’t want the FBI knocking on my door because my IP has been tied to some kind of kiddie porn site.