Firstly we don’t actually know who these people are. The Syrian rebels are essentially everyone in the country that doesn't support Assad from liberal students to Al Qaeda. The later are not the sort of people we should be arming. Also their numbers specifically are growing as terrorists from across the Middle East are journeying to Syria to destroy Assad’s regime. We don’t really know the strength of each of the Syrian Rebels groups, we can only pick out individuals who are in some way leading the civil war.
Also do we really need to arm the rebels? The Saudi’s and Qatar are already doing so and sure they are only sending hand held weapons but it’s not like we’re going to be sending over tanks to the rebels. Also the Turkish are very key to this. They were very close to going to war with Syria last year and its likely tensions will rise again. They have been indirectly helping the rebels for ages in as many ways as they can and it’s possible they may set up ‘safe’ zones in Syria where the rebels can safely stay. This would allow for a base to be created from where they can launch attacks in a very similar way to the no fly zone in Libya, which allowed ½ of the country to be controlled with little violence by the Free Army.
I won’t pretend that everything is going well in Syria for the rebels. This is a civil war and they are always long and brutal. This will make the country of Syria and is likely to start a path in the future to a more democratic country. But should we help them to the extent of arming them. No, it’s too dangerous on our behalf. Even if we did do this the path to freedom for Syria will be just as long and bloody, even after the war is over.