Yeah, Esther's right on the money here. Quit with the stupid justifications. No one buys it.
That said? I like Power Girl's cut-out ("boob window") costume. It was stylish when she was introduced, and now it's retro. It's actually very classic looking and when originally designed it was actually pretty classy looking too. The design is just plain good. The design is actually great, I'd say. I'd wear it if I could pull off white myself.
That's why they keep going back to it, because it's a good basic costume and as it was originally just a small cut-out on an invulnerable character it's not inherently lewd/impractical. (Unlike the midriff-baring Huntress, or the monstrosity Carol Ferris is parading around in--though my hat's off to Mahnke for making it less eyesearing.) All the attempts to change it have had her going to worse costumes. (The one with the normal neckline actually tends to show even MORE boob than the cut-out.) And it doesn't need a reason any more than she liked the look better than any emblem she tried to put there, and now she's just used to it. Anything beyond that is downright insulting, like you're trying to fool us into thinking there's something inherently empowering about baring your breasts. There isn't.
(We all know good fashion isn't dependent on the amount of fabric. Different cuts do different things for different bodies. And that's not even getting into color. Aesthetics are complicated in this area.)
Now, if DC feels guilty enough that they feel a need to justify this costume, maybe rather than offer us some bullshit they can have the artists draw it tastefully. A cut-out is ideally supposed to offer just a hint of cleavage, not go down to or below one's nipples. Just a guess, but that and the annoying high-cut bikini bottoms might be where all that guilt and disgust originates.