This is not a valid argument. Anything can be used for evil, but that doesn't mean we should avoid or outlaw everything.
A knife can be used to cut a chicken, it can also be used to kill someone. You would not deny your neighbour when he asks to borrow a knife because "you could kill someone with it".
The OP doesn't want to enable the bad uses of Tor, nor do they want to get into legal trouble for it. It's demonstrated that by running a Tor exit node, you are at a high risk of the former and at least some risk for the latter. Both carry significant costs. By not running a Tor exit node, you eliminate these risks to yourself.
The risk that your neighbor will use your knife to kill someone is far lower by comparison. Additionally, the risk that there is a legal threat should they choose to do so is also quite low.
Depends on your location and your definition of "legitimate". If you define "legitimate" by what your particular government says is OK, then no, you won't find yourself in court for those uses. Unless you get extradited to a government that has different opinions.
A knife can be used to cut a chicken, it can also be used to kill someone. You would not deny your neighbour when he asks to borrow a knife because "you could kill someone with it".