Is there a reason to ignore the decree to pound the pillars?
Is there anything I miss if I don't "pound the pillars" in the basement of the castle? Am I making any of the stars inaccessible by doing so?
Solution 1:
Yes, you'll miss something if you don't pound them; no, it has no negative effects.
Pounding the pillars drains the moat around the castle, allowing you access to the Vanish Cap level. That level has one star, from the 8 red coins.
Solution 2:
You can safely pound the pillars, you will gain access to new stars. And as a matter of fact, no star is missable, you can still pound the pillars later.