This reminds me of the Shakespeare quote " . . . the heresies that men do leave are hated most."
Lots of my evangelical friends think I am emerge-ish and several of my former college friends are pastors of evangelical emerging churches, so I'm sympathetic to what you're saying about the emerging impulse being a critique of one's own tradition, a prophetic voice coming from within the family. There are those whose voices sound very much that way to me - a loving and concerned critique from within the family. Sider, Noll (re. anti-intellectualism), Weber, Rob Bell even.
But at the same time as I keep pointing out, much of the language used by other leading voices in Emergent (especially as present on the internet, which is where I primarily find it)suggests, invites, perpetuates, an us/them dichotomy rather than discouraging it. Maybe as you say it really is a critique of "how I used to think" rather than an intentionally other-focused critique. But because you no longer think that way, it really isn't a critique of yourself, but rather of people who are still so benighted as to think the way you used to think before you learned better. That's a much different thing than a true self-critique. Is a fundamentalist who used to be a "drunken fornicator" prior to his conversion, and who now rails against "drunken fornicators" and calls them to repent as he did, really doing anything spiritually different than someone who used to be a Republican but now ridicules George Bush, rails against and calls conservative republican Christians to repent? Calls to repentance are well and good, but when speaking like that, we are doing something other than "taking care of the plank in our own eye."
If what we are critiquing is no longer something that we believe or practice then we are speaking prophetically, perhaps from personal experience. That prophetic voice is legitimate and much-needed, but let's not confuse it with self-critique or plank-finding. And let's make sure the real self critique (of my current self, not just my former one) is still going on, as I suggested on Julie's blog. Not merely the condemnation of "those with whom I will never more be confused if I can help it." As you point out, you (and even many still-evangelical emergers) often seem to have much more in common (i.e. are much more likely to be confused with) people outside the evangelical family, than within. That's ok and maybe even a good thing, but if it's the case then self-critique is something other than criticising the culture with which you no longer identify. And you gain a lot more credibility with the family members who you are criticising, if they don't feel like they are the ONLY people with whom you see anything wrong.
I was typing fast and casting about for various 'isms to make a point. Obviously Communism is a poor example (though I struggle to see what charitable or logical purpose was served by your pointing that out), as most academics and Boomers who eagerly embraced communism a few decades ago have either opted for bourgeois capitalism after all, or have quietly dumped communism for other, more fashionable ideologies now in academic vogue, or both.
You say: "I think that's because I place a lot less weight these days on agreement over metaphysical questions and a lot more weight on agreement over ethical questions."
That resonates with me quite a bit. Whether you agree with their theology or not, I expect you are familiar with the term used often by Schaeffer and since by Colson and many others, of co-belligerence. That cooperation with others for a common moral or ethical cause important to both is, at least in part, what you seem to be talking about even if it's on matters other than the "culture wars" issues Schaeffer usually spoke of. At the same time, where do you go with the observation that even those who agree over ethical questions often fail to live up to their own high ideals? The major world religions (and even a religion disavowing that it's a religion, like Atheism) generally agree on most questions of ethics. The golden rule isn't unique to Christianity. But where they part company is what to do with our self-knowledge that no matter what we do, we don't measure up to what we know we should be. Don't you kind of have to get metaphysical there, whether you agree with a particular X'ian theory of the atonement or not? And don't bedrock assumptions about metaphysical issues end up driving real-life, on the ground stuff as well? You see it pretty clearly in fundamentalism. It would be odd if fundamentalists and hyper-calvinists were the only ones whose metaphysical assumptions produced unhealthy results down the road for themselves and the world around them. I have atheist friends, too. But their no-god assumptions seem, to me, to have equally ugly end results as do the metaphysical assumptions of fundamentalists, even if the atheists are nicer and closer to the spirit of Jesus than many conservative X'ians (and actually, if you both stay away from metaphysical issues, you can have a great time with plenty of fundamentalists, too).
I don't think metaphysics should be in-your-face, but I don't think you can escape them for mere agreement on ethical issues either; at least not permanently. Can you?