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)

The danger is this easily degenerates into hypocrisy which corrupts the soul and turns into worse things. The hidden motive doesn’t even need to be selfish. It can even be noble or selfless as it is with naive Straussians/Great Man theorists. So long as there is a gap between visible and hidden postures, corruption can sneak into the gap.

Otoh Neal Stephenson argues hypocrisy was the greatest virtue of virtue of Victorian culture.