The scary thing about Asch's conformity experiments is that you can get many people to say black is white, if you put them in a room full of other people saying the same thing. The hopeful thing about Asch's conformity experiments is that a single dissenter tremendously drove down the rate of conformity, even if the dissenter was only giving a different wrong answer. And the wearisome thing is that dissent was not learned over the course of the experiment—when the single dissenter started siding with the group, rates of conformity rose back up.
Being a voice of dissent can bring real benefits to the group. But it also (famously) has a cost. And then you have to keep it up. Plus you could be wrong.
I recently had an interesting experience wherein I began discussing a project with two people who had previously done some planning on their own. I thought they were being too optimistic and made a number of safety-margin-type suggestions for the project. Soon a fourth guy wandered by, who was providing one of the other two with a ride home, and began making suggestions. At this point I had a sudden insight about how groups become overconfident, because whenever I raised a possible problem, the fourth guy would say, "Don't worry, I'm sure we can handle it!" or something similarly reassuring.
An individual, working alone, will have natural doubts. They will think to themselves, "Can I really do XYZ?", because there's nothing impolite about doubting your own competence. But when two unconfident people form a group, it is polite to say nice and reassuring things, and impolite to question the other person's competence. Together they become more optimistic than either would be on their own, each one's doubts quelled by the other's seemingly confident reassurance, not realizing that the other person initially had the same inner doubts.
The most fearsome possibility raised by Asch's experiments on conformity is the specter of everyone agreeing with the group, swayed by the confident voices of others, careful not to let their own doubts show—not realizing that others are suppressing similar worries. This is known as "pluralistic ignorance".
Robin Hanson and I have a long-running debate over when, exactly, aspiring rationalists should dare to disagree. I tend toward the widely held position that you have no real choice but to form your own opinions. Robin Hanson advocates a more iconoclastic position, that you—not just other people—should consider that others may be wiser. Regardless of our various disputes, we both agree that Aumann's Agreement Theorem extends to imply that common knowledge of a factual disagreement shows someone must be irrational. Despite the funny looks we've gotten, we're sticking to our guns about modesty: Forget what everyone tells you about individualism, you should pay attention to what other people think.
Ahem. The point is that, for rationalists, disagreeing with the group is serious business. You can't wave it off with "Everyone is entitled to their own opinion."
I think the most important lesson to take away from Asch's experiments is to distinguish "expressing concern" from "disagreement". Raising a point that others haven't voiced is not a promise to disagree with the group at the end of its discussion.
The ideal Bayesian's process of convergence involves sharing evidence that is unpredictable to the listener. The Aumann agreement result holds only for common knowledge, where you know, I know, you know I know, etc. Hanson's post or paper on "We Can't Foresee to Disagree" provides a picture of how strange it would look to watch ideal rationalists converging on a probability estimate; it doesn't look anything like two bargainers in a marketplace converging on a price.
Unfortunately, there's not much difference socially between "expressing concerns" and "disagreement". A group of rationalists might agree to pretend there's a difference, but it's not how human beings are really wired. Once you speak out, you've committed a socially irrevocable act; you've become the nail sticking up, the discord in the comfortable group harmony, and you can't undo that. Anyone insulted by a concern you expressed about their competence to successfully complete task XYZ, will probably hold just as much of a grudge afterward if you say "No problem, I'll go along with the group" at the end.
Asch's experiment shows that the power of dissent to inspire others is real. Asch's experiment shows that the power of conformity is real. If everyone refrains from voicing their private doubts, that will indeed lead groups into madness. But history abounds with lessons on the price of being the first, or even the second, to say that the Emperor has no clothes. Nor are people hardwired to distinguish "expressing a concern" from "disagreement even with common knowledge"; this distinction is a rationalist's artifice. If you read the more cynical brand of self-help books (e.g. Machiavelli's The Prince) they will advise you to mask your nonconformity entirely, not voice your concerns first and then agree at the end. If you perform the group service of being the one who gives voice to the obvious problems, don't expect the group to thank you for it.
These are the costs and the benefits of dissenting—whether you "disagree" or just "express concern"—and the decision is up to you.