"voluntary trade" makes it sound like said trade wasn't actually illegal (in 

   other words, like something the police are actually supposed to stop, peaceful 

   or otherwise.)

No it doesn't make it sound like that. "Voluntary" is not synonymous with "legal". The quality of voluntary trade is that both parties to it want to be in it: it's consensual. Many consensual actions are illegal, and some would argue that is oppressive.

    Left completely unmentioned, is the fact that Bitcoin is designed, and intended, 

    to make it infeasible to track users and enforce laws against transactors. 

Yet they tracked Ulbritch, who was using Bitcoin and Tor. If they dedicated the same amount of resources to catching this extortionist, I think it's pretty likely he would be found.