I suppose it's that deriding stay-at-home parents is commonly and socially acceptable (in media, articles like this, etc), more so than in the other direction. I can't think of an example, e.g. in media or press, where the working mother is ridiculed.
But anyway, it's a matter of perspective, I suppose, and which social bubble one inevitably inhabits.
No, it's 100% NOT socially acceptable to tell a so-called "stay at home mom" that she's anything less than a hero who's the best person ever (even if she doesn't actually do very much all day). Working outside of the home is very much looked down upon as something unfortunate that one has to do.
Coming out and actually admitting that you desire to go to work rather that you have to is incredibly socially unacceptable for a woman. This sort of statement might even get CPS called on you if the wrong person overhears it.
This wasn't so much the case 15 years ago, we have turned into a society of child worshipers.
But anyway, it's a matter of perspective, I suppose, and which social bubble one inevitably inhabits.