One meta belief I have, is that I think "on the face pursuing idealistic objective A, but actually being tilted toward selfish objective B" is better than "openly pursuing objective B".

Many seem to believe the opposite, typically saying something like "at least the latter is honest".

I feel like what this misses, is that maintaining the face of pursuing idealistic objective A, and using A to coordinate a large coalition, is a pretty big speed bump against attempts to pursue B too brazenly. When "the mask comes off", things actually become much worse, and strategies that pursue B at high costs to other values (including A, and also often general human decency) become unlocked.

Are there any good arguments against this intuition I have? (Whether generalized, or about specific situations)

One counter is that hypocrisy can actually enable worse behavior. If you already have a cover story, why not go big?

Here in SF we have city services nonprofits with flowery mission statements, where many of them are effectively embezzlement fronts ($1b/year from the city budget). Would they have gotten away with it as long as they have as normal for-profit contractors? Probably not.