There is a real possibility when Assad senses the end is near he will attack Israel in an attempt to be seen as a hero and if the west ever does use military action Assad will retaliate against Israel anyway so lets carry out a preemptive strike take the war to him on our terms. There is also the fact nobody knows who will replace him and it could be a radical regime or lead to an increase in terror we can't assume it will be a peace loving government. It is a fact that Assad has the largest stockpile of chemical weapons in the region and we don't want those or the Scud missiles falling into the hands of a radical regime or terrorists so preempt we can make sure all these things are destroyed. A preemptive strike would not only be good for Israel's security but it is the right thing to do. Syria might be an enemy and they have no love for us but Israel with all its military muscle cannot standby and watch Assad massacring thousands in a bid to hold onto power, this isn't civil war its murder and because of a mixture of domestic & international politics the west will not intervene so Israel should create a situation which will help make it easier for the west to attack Syria.... Israel attacks Syria as a humanitarian gesture because nobody else will help ( some Syrians might even appreciate it ), Israel destroys all the military targets its worried about falling into the hands of terrorists or a hostile post Assad regime. Israel then makes some efforts to stop Assad using air power ( not a major ground offensive ) at the same time it talks to the western powers and says look we started this now you get your act together form some kind of UN peace keeping coalition and finish the job. At the very least even if the west don't intervene whilst Israel is keeping the Syrian army busy it will give the rebels the room they need to go on the offensive.
Five people hurt in fire at Germany refugee station (Reuters)
from the article: Lieberman: Israel would offer aid to Syrians if asked