I don't claim to have any expert insight into Syria. All I can go by is what I've read, and by what I've been told. On this basis, I find it difficult to disagree with Seymour when he says it's a popular uprising. At least, it's definitely a popular uprising amongst the Sunni population of Syria. Much of the coverage, as Angry Arab (criticised in Yassin Kassab's first paragraph) has repeatedly pointed out, has been viciously anti-Alawite, often without any thought whatsoever being put into the underlying message it sends. 16 months into the uprising, you would have thought by now that we would have had some definitive reporting on just what section of the population supports the status quo and which supports the revolution. I say status quo and not the regime for the reason that it seems unlikely that anyone now has much love for Assad, but they understandably fear what might come next. Some of this will be down to the regime's constant propaganda, claiming that all of those in support of the revolution are al-Qaida supporters, while some will be down to very real fears of the possibility of reprisals should the uprising succeed in overthrowing the Ba'athists.
We don't know then just how far the uprising is supported by the Alawite (including other Shias), Christian and Druze minorities. It could be that they're just keeping their heads down and secretly hoping for it all to be over quickly, and will adjust accordingly whichever side eventually triumphs. It could be that there's a sizeable minority among them who support the revolution, but can't do so openly for fear of what will happen to them. It could be that they're completely opposed to the revolution and dearly love Assad and wish to retain their status, or it could be that they'd rather have Assad, murderer as he is, than either the Muslim Brotherhood or an even more fundamentalist Islamist grouping in power. The point is that we just don't properly know. Of all the protests associated with the Arab spring, only Bahrain comes close to Syria in terms of how religious background impacts as heavily on whether or not someone is likely to be for the uprising or against it.
What both Seymour and Yassin-Kassab underplay is the role of Saudi Arabia and Qatar in funding and supplying the revolutionaries with weaponry, with the Turks and the Americans playing a more minor role. It may well be that this is still relatively slight in comparison to the equipment being supplied to the Syrian military by Russia, but it surely isn't a coincidence that the fighters have made major gains since the House of Saud and the Qataris upped their game. Both countries simply would not fund or supply fighters unless they were fairly sure of what they were getting themselves into; they tend not to throw guns and cash around as freely as the Americans have in the past. The Saudis have little time for the Muslim Brotherhood, regardless of past ties, as shown by their antipathy to the coming to power of Mohamed Morsi in Egypt. Qatar may have trained the forces that made the difference in Libya, where the West has claimed that a "liberal" grouping won the elections (if you can call a massive coalition which has Islamists within it liberal), but they too wouldn't be getting involved if they feared a government opposing their regional influence coming to power.
It's impossible then to ignore the fact that a major contingent of armed groups operating in Syria are at the very least Islamist in outlook, while some are straight jihadist or Salafi. This is to be expected when Islamism has long taken over from various strains of leftism as the main political resistance in the Arab world to secular authoritarian rulers, but this doesn't mean we should be any more accepting of jihadists than we were, say, in Iraq. There the likes of Seymour overlooked the fact the much of the resistance was made up of jihadists (The Islamic State of Iraq and Ansar al-Sunnah/Islam, to name the two major groups), with only one or two insurgent alliances being nationalist in politics, as they were fighting the Americans, despite how they succeeded in sparking civil war through sectarian attacks.
While it would be lovely if the Free Syrian Army was overwhelmingly secular and non-sectarian, this was unlikely to ever be the case when the regime has also turned towards sectarian attacks through desperation. All the same, it makes it impossible to support the FSA when you can't possibly know what will follow should Assad fall. At the same time, you can completely be in favour of the overthrow of Assad and his murderous clique by those sections of the opposition that simply want to be rid of a tyrant determined to cling onto power at any cost. Regardless of misgivings about the electoral triumphs by Islamists in both Tunisia and Egypt, I challenge anyone to deny that their being in power is vastly preferable to the despotisms of Ben Ali and Mubarak. In both countries however the state remained while it was the rulers who were overthrown. In Syria, like as in Libya, should Assad be overthrown the victors will have to begin from scratch, except the inevitable sectarian tensions that will follow will make the regional spats between militias in Libya look like a picnic. Syria is one of those instances where the third way is the best way: for the revolution, against sectarianism.