One of most popular argument used by those in favor of an intervention in Syria is that if we leave the arming of the rebels to the Saudi's and the Qatari's they will arm their friends - Salafi, Brotherhood supporters and other radical Muslims. So - they argue - we should arm and support our friends: the moderate Syrians. Otherwise, when everything is over and the rebels have won it is the radicals who will dominate.
There are several errors in this thinking. The first is the assumption that it is desirable that the rebels will win. Assad has at least 20% of the population behind him and maybe much more. If the rebels win these people will become second rate citizens - something irreconcilable with democracy. So if you want to have a democratic Syria one should strive to reach some compromise between the two sides. As an additional benefit it will prevent a lot of bloodshed.
A second error is to think that a smaller group of Jihadi's is less dangerous. Tunisia had no fight and the extremists did poorly at the elections. Yet nowadays armed Jihadi group dominate the scene. Most selling points of alcohol have been closed and more and more women cover their head. Actually this is a rather normal pattern: in many revolutions (for example Russia (1917), Fance (1789) and Iran (1979)) after some time a radical minority grabs the power. This very probably stems from the fact that a revolution legalizes the principle that power comes from the mouth of a gun.
Neither should one forget that just as the communist of yore the Jihadi's believe that any means is justified to reach their goals. If they believe it will help their cause they will be happy to kill some of those moderate leaders.
A third error is to think that those moderate Syrians will blame it on us that we don't give them enough weapons. According to this logic they will always blame us when we don't help them enough to win. They know we can win the war for them so some of them will always blame us for not doing their bidding. But it is their fight and it is their decision not to compromise and instead to adopt radicals who antagonize a considerable part of the population. We should not reward them for that.