For social conservatives, intentionally lying about one's social views isn't really an option. The idea of someone being ardently pro-life but feigning support for abortion in order to win power and then enact changes in their favor is, by and large, alien reasoning. The thought doesn't occur to them. They can be accused of being ignorant, of stupidly misrepresenting or misunderstanding one or another line of evidence, and certainly they play their share of rhetoric games. But no one ever looked at Mitt Romney and thought 'He's probably secretly pro-life, and was just favoring abortion for the liberal crowd!' If anything, the suspicion was that he was even worse than he let on.
For "progressives", lying about these sorts of things is second nature.
Go talk to "progressive" atheists, and most will tell you as much. Obama? He's an atheist. So's Politician X or Y or Z. He's just lying about his beliefs because he wants to get elected. Bill Maher said as much outright, and I believe PZ Myers said the same. There's no real shame in the accusation, because it's not an accusation coming from them - it's just the way it is. Want something, but being honest will deny it to you? Just lie. What are you worried about? Morality? Ends justify means. Or pick whatever other flavor of morality that says you can lie to get what you want, and there's a good number to choose from.
Now personally, I've seen this firsthand time and time again - and not just with "progressive atheists". I've seen progressive Christians tearfully advise giving up the fight on gay marriage as a lost cause, informing everyone of how we can revisit the issue later when fortune favors us and to 'pick our battles wisely', only to get cornered and admit yeah, they're in favor of gay marriage and they'd fight bitterly against anyone who refused to legalize it. I've seen progressive Christians adamantly insist that it's wrong and immoral to pass laws with religious beliefs in mind, then spin around and say it's immoral to oppose such and such a law because Christ would have wanted it that way. I've seen lie upon lie upon lie, and that's not counting the times I've seen blatantly obvious lies with just the barest shred of plausible deniability.
I know this seems like I'm Mister Conservative bashing The Enemy. But really, I'm just relating what experience has taught me, from talking to progressives personally, to watching them in the public sphere. For social conservatives, lying - not 'being wrong', but literally, willfully lying - is shameful. For progressives, it's only a bad thing if you get caught, and then only if it does damage to a given goal.