Cameron made his case. Politically it was attractive. Strategically it was very weak. This is the key. Britain and its allies in the West, especially the US, stand at the head of a string of failed military interventions which although produced an apparent initial military victory, caused the failure of everything that came after. Libya, Iraq and Afghanistan are failed states with governments split and in only partial control. The terrorist threat is now many times greater that it was when this project began post 9/11. There is already concerted bombing by America, France and Russia and although there is a rumour that the RAF has a weapons system with unique properties on its Tornado jets, which even the Americans cannot match, this is not a material military factor. The skies above Syria are already congested adding to the hazards of war.
Militarily voting yes to bombing Syria requires the following conditions to be met. First there must be a full agreement for a coordinated military campaign among all the engaged powers, namely Russia, the US, France, Britain, Iran and other members of the US coalition. Second, the various backers in the Gulf secretly funding and arming IS must be told to stop or be threatened with a freeze of their financial assets in the West and an embargo on the sale of their oil. Third, there has to be a clear focus on a single enemy; Islamic State. This fantasy about moderate opposition groups has to stop. Were these so called groups to defeat Assad, they would fall out among themselves and the only certain thing is that IS would occupy Damascus within days. They should be given a choice. Either join and fight IS and IS only or be regarded as an enemy. The reward for them is to be part of the political settlement in Syria.
The political settlement, which must be integral to the military assault, can only happen if the West drops its opposition to Assad going before it is agreed and the Russian hint that he might stay on afterwards. This will presumably lead to properly supervised elections for a new President and Assad should be allowed to stand if he wants to but not if his authorities have anything to do with running the poll. The West has to accept that Assad is the price for containing IS. Without his powerful army on the ground leading the various other forces willing to engage IS, the air campaign is a waste of bombs.
Finally, and this may be the most important point of all, it is essential that part of the political settlement is a new deal, probably an autonomous homeland, for the Sunni minorities in Syria and Iraq. The reason IS, with a few thousand fighters, has been able to rampage across the region is because the Sunnis have at the least stood aside and more often extended the hand of welcome. However much it is pounded and driven from hither to thither, IS will not cease to be a potent threat until it loses the tacit support of Sunnis and that will not happen until they get a fair deal.
None of this is in place yet so the proper vote is NO. The biggest disappointment in Cameron arises from his assertion that British bombing of IS in Syria makes the UK safer. He knows that is not true. In the short term the risk of terrorist attack rises and British civilian dead are a real possibility. Brits have put their lives on the line before in the cause of freedom and paid the price, but it is very wrong to make these misleading assertions to bolster a case full of holes.