You win the prize. Voltaire is correct.
http://www.quotationspage.com/search.php3?Search=if+god+did+not+exist&startsearch=Search&Author=&C=mgm&C=motivate&C=classic&C=coles&C=poorc&C=lindsly
Yippie! What do I get? :)
It was not Voltaire. It was Robespierre, during the French Revolution. He was a French lawyer, no less.