Thank you all for a mostly constructive debate so far, I have given rep to posts that I think move the conversation along or add a decent point. Thanks in particular to Sandro sticking an (admittedly off topic) oar in to help clarify a point on PowerPlay.
I see Piracy as a point where karma and C&P collide. It is intended gameplay but obviously against the 'lore' law, it is the piggy in the middle.
I'd like to furiously agree with babelfisch & several others that to be pirated is a consensual act, as a pirate you may be able to force a player to give up some cargo once, but after that it is up to that player to stay in Open & subject themselves to it again if they didn't enjoy the experience, and a fundamental part of that is to survive the encounter if the result is not a legitimate PvP fight.
The Trader faces a dilemma when they pass through pirate territory. Is it worth the risk? The Pirate currently does not face anything like the same dilemma, if the operation goes bad they just gank the hapless victim & find another target.
It should be as much of a dilemma for the Pirate as the Trader; A kill should be a last resort if the trader does not deploy hardpoints. You should really, really not want to kill them. Be the cat & toy with your prey - get their shields down but let them low wake (they escape by the skin of their teeth, awesome) & you give chase & pull them out again (oh sh...). Persuade them you only want a little cargo, maybe offer to escort them to dock so you can both contribute to the CG etc.
Perhaps it's also worth taking CLogging out of the equation, it's tied up in the same Karma system after all. Suicidewindering your bounty away appears to be undesirable behaviour too.
Piracy as others have said is more or less a voluntary, end-game activity. It requires a comprehensive understanding of the game and a non-PvP meta ship, to pirate successfully is more about providing a thrilling experience for others than the actual cargo, if anything the cargo is your reward for putting on a good show.
It seems to me that Sandro is of much the same opinion, but he is in a position where if a solution cannot be found, he may have to make proper Piracy obsolete if patterns of behaviour cannot be distinguished from more toxic actions.