The rebels have allies with jihadist groups like Ahrar al Sham which praised the Taliban, and said democracy is for infidels,Jaish Fateh al Sham which is formerly al Nusra aka Syrian Al Qaeda is an ally of the rebels, Ajnad al Sham, Turkistan Islamic Party which is a foreign fighters group. They used suicide car bombs in the recent West Aleppo offensive last week. So in all the rebels will replace Assad's secular tyranny with religious tyranny. They have said they will genocide the Alawites,Kurds,Druze and Christians.
If the rebels were a benevolent force then how come the Kurds,Alalwites,Druze and Christians haven't joined them? Syria is not a simple black and white issue where Assad bad and rebels good. It is a complex sectarian war we have no buisness to get involved in.