"You can't have your cake and eat it, too!"
Why the hell not?
What idiot thought up such a phrase to apply it to something that was bad? Why the hell should I have cake if I can't eat it, too? I want pie and meat and potatoes and gravy. Am I supposed to sit and stare at a table full of food begging me to eat it like some kind of monastic self-flagellator?
I don't think so, Kemosabe. I make my own culinary choices, I'll have you know!