This is crazy, but I'd only arrest those who harm or seek to harm or diminish somebody's life, health, property or privacy. Oh and those who risk the life, health, property and privacy of others via sheer carelessness, impairment or disregard.
I know part of the job normally requires busting harmless college kids who buy dime bags and catching adults who pay other adults for sexual acts that they could legally exchange for free, but I'm wild and crazy like that I guess.