I value privacy and support VPN use, but for some reason this seems different to me. Maybe something to do with a VPN being a company using servers to create an obvious layer of identity protection that police can generally subpoena when of importance.
By running a Tor exit node, this individual was consciously allowing his IP address to be used for potentially malicious purposes. Why can't it easily be compared to someone making a cover for or assisting a criminal they don't know the identify of, which would be a crime if committed in person? Investigations lead back to him because he put himself in that position.
analogy: VPNs seem like concealing your ID from everyone, however police can sometimes work to see it if a court deems it justifiable and necessary. Individuals running Tor exit nodes seem like being given someone else's ID instead, with no trace otherwise.
Untraceable VPNs (ones unaffected by subpoenas) are somewhere in the middle, but the primary issue I see with this is the Tor system's use of someone else's ID rather than hiding your own (investigators are aware when they find a VPN service's IP).