I don't care about "public approval" or "who can or can't sing it" (but I CAN think of a few Elphaba's who probably shouldn't be singing that role) Again, not the point. An actor who sings has a responsibility to his or her instrument; and the longevity of that instrument. If they choose to blow out their cords playing Elphaba, 8x a week, that's their own prerogative. But you run the risk of having a not so great voice as you age.
There are a lot of examples of this, but I'll just bring up one: Patti LuPone. She openly admits to the fact that her voice was not the same as it was 30 years ago when she was singing Evita. But luckily she found a great vocal coach (Joan Lader) who was able to teach her some healthy technique that has saved her instrument really.
Bottom line is, its a gift. Use it sparingly folks. Its fun to whale those high belt notes, but do so with proper technique otherwise it won't be there long.