Its got nothing to do with gay rights, democracy or even chemical weapons. Its about regional influence, oil and mostly: gas.
In a nutshell, back in 2009 IIRC, qatar wanted a pipeline from its rather recently discovered massive (actually, world's largest) North Dome gas fields to the EU. This pipeline would go through SA, Jordan, Syria to the Mediterranean and/or Turkey. Syria refused, because it would threaten the stranglehold its Russian ally has on the EU gas market though Gazprom. Instead Syria pursued an alternative pipeline from Irans South Pars gasfield (actually the same gas field, but on Irans side of the persian gulf) through Iraq to lebanon and the Med, with an option to connect to Turkey. A $10B deal that was signed in 2010. Not much later, the "uprising" began. No coincidence.
Qatar and later SA fund the "rebels" (better word is jihadists or mercenaries) for billions of dollars to get rid of Assad and install a more sunni friendly regime. Failing that, plan B is to split the country in 2, allowing the north/eastern "free Syria" to run the qatari's beloved pipeline to the EU, instead of Iranian gas flowing to the EU. Thats whats going on. The vast majority of "rebels" arent even Syrians, they are paid mercenaries from all over the world, and most of them religious fanatics generously paid for by the Saudi's and qatari's.
The US really doesnt really have a horse in this race, except placating to its allies saudi arabia and israel. And weakening Iran and not allowing Iran to sell gas to the EU, although the only real reason the US wants that is because Israel wants it. As for Israel, it doesnt want a Saudi controlled extremist sunni regime at its borders, but it doesnt want a strong Assad supporting Hezbollah (and Iran) either. Lacking a better option, Israel wants perpetual war in Syria, weakening all fractions, including Hezbollah.
I also heard that hypothesis already, and have to say I find it the most reasonable explanation at the moment.