The discussion on News Night last night (Ming Campbell et al) asked the relevant questions about intervention: What are our objectives? What are the risks? What certainty do we have that the situation will be made better?
The only question I imagine Cameron has asked is the first one, and come up with the same wrong answer as other post-war PMs (starting with Eden and ending with Blair. Please note, I don't include Thatcher in this list): Britain still has influence and I want to be seen walking the world stage (and, of course, keep in with the Americans).
There seems to be other joint delusion that we understand and can influence events for the better in the Middle East, that somehow they think and will react like us. Look at the Arab Spring welcomed by the great and the good everywhere. Take Egypt. Get rid of nasty dictator, have free elections, result harmony and progress. Changed our mind pretty fast on that one, didn’t we? New doctrine: free elections good; military coups better.
I think we should stay out.