Perhaps it might be easier to say: the number of deaths can be placed in a simple equation which shows how much war and how many American deaths (and any other significant factors such as the cost to tax payers and through-put onto the economy, positive and negative) a country as a whole is prepared to accept to have cheap gas (petrol). Anti-war protest is one thing: having the ability to make decisions about when or if it is wise to stop, quite another.
Petrol prices does apply to Britianm, but continued guaranteed supply does. We British already pay through the nose (roughly 2 1/2 times as much as U.S. users at $7 as compared to $2) by dint of the high national tax levied on fuel. Our dead (and how many we are going to tolerate) could also be tied in with the benefits British companies get from us remaining in Iraq.
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Although no one take away the saddness and devastation of the parents of soldiers who died in Iraq, and Iraqis orf Iraqis, it is these factors which have to be placed in the the scales.