Who's to blame?

When the right has a policy, they are to blame for any violence that may come out by people who are against the policy. But when the left has a policy, the opponents are at fault for the violence.

NY Governor David Paterson suggests that the reason a Muslim Cab driver was stabbed in NYC, is the debate over the Ground Zero Mosque.

I don't think the stabbing has anything to do with the Mosque, but I do wonder why here is the blame is on those are against the move to build the Mosque, but back in Arizona -- when people placed Nazi symbols on government property -- it was the fault of those who made the tough laws?

Same thing was with former US President G.W. Bush. HE was always to blame for the divide in the country, but not his opponents who were against him at every step of the way. So my question is: When is violence the fault of the policy, and when is it the fault of those against the policy?