Withholding your criticism, however, will just turn you into a mostly worthless zero-contributor.
Don't dump criticism - dump tactlessness.
Here's a simple trick: Instead of saying "You're wrong, because X Y Z" (which is also my natural tendency, as you can see from these posts!) try using the formula: "I see what you're saying. A B C (rephrase what they just said). Hmm. What about X? Does that have any impact?" and let them get to Y and Z themselves.
Just using that phrasing will help you tremendously. Of course there are other even more subtle ways to do it, but this works for most situations, and once you get started down this path, you'll figure them out.