Personally for me it is about the traffic that may be routed through my computer by the Tor network - I definitely do not want child porn, drugs or terrorist related site transactions packets to even touch my computer. It maybe a rare occurrence, but I want certainty. If we could control the traffic that is allowed on our network / computer, I'd be a more willing user of Tor. (A use case example would be to allow a Tor user to create a white list of onion sites from which they would be willing to accept traffic).