One thing to remember is that there is a case of a warden losing her taint (wow, that sounds dirty). And it's Alistair's mother, too. Though whether or not Alistair is aware of this is another thing entirely, and, let's be honest, he probably isn't.
If he was, then the HoF's quest to cure the Taint wouldn't be necessary if the Architect was still alive. So I'm going to guess he's not.
I guess the big difference between Golems and wardens is that wardens are necessary. 2 golems could never do what Alistair and the Warden did (and Riordan, everyone always seems to forget that guy) Golems are usually made either from a selfish desire to dominate (both the power of the golems and the threat of becoming one) and with no regard for human life. It's expediency vs necessity.
I considered raising this point. It is a valid one, but can't be used to defend Alistair since he didn't know about it at the time he asked you not to use the Anvil.
Another thing is that the Wardens do actually let you back out, up until you learn of the joining, whereas people who are being turned into golems often have no choice in the matter to begin with.
Not always. Daveth had no choice, and the Warden PCs who had been saved from some horrible fate using the Rite of Conscription probably didn't either. (At least legally speaking, since surprise surprise: in DA:I we learn of a conscript saved from the gallows who deserted.) I'd actually imagine none of the PCs did, since even the ones who came willingly were probably subject to Conscription if they looked like they were backing out due to the amount of promise Duncan saw in them.
Which is funny, because the joining seems to be public knowledge by Inquisition, so Jory was basically killed for nothing. Oops.
It varies. Anora knows one of the really sensitive bits as of late Origins, and while it's not clear who heard her say it and who didn't she didn't seem to be troubling herself to keep her voice down. In Inquisition the NPCs who know the secret kind of dance around it as much as they can (which eventually becomes not much at all given that you wind up in it up to your eyeballs,) and the false Blackwall is (in retrospect) obviously pretending to know but be unable to tell.
Well, we did have the divine's spirit. It's not impossible for Wynne, or at least her spirit to make a comeback in future games.
Wynne coming back as a ghost is a maybe, though given that with ghosts it's usually ambiguous whether it's a spirit impersonating them or the real deal I doubt it. There's only one obvious spirit who'd impersonate Wynne, and that spirit doesn't have time to ghost about. (Though maybe if we meet both Evangeline and the spirit, and meet them as separate characters, the spirit will take Wynne's form?)
I think Blackwall references that conscription and the ancient contracts are only as useful as a clever tongue makes them - I mean, what will the wardens do if you refuse? They're going to save the world anyway, and they are neither petty enough or have enough free time to really hold it against anyone. Nor are they foolish enough to damage their diplomatic ties with everyone. And they need committed recruits, or else they'd be the Night's Watch.
What Blackwall says is that Conscription is only as binding as a clever tongue can make it when there isn't a Blight on. That's not the same as people being free to leave during a Blight, and certainly isn't the same as Duncan being willing to let Daveth or the Warden PC leave, for example. To be sure Duncan steps carefully around people who might take offense to his actions, but by the time you get to Ostagar you have nobody protecting you no matter what your Origin is. (Edit: And this assumes the false Blackwall's word on these matters is accurate, which we can't.)