Well, scams are unethical regardless of method used. It would equally unethical if done by a human. So that's not the difference.
And Impersonators are already profiting off of someone else, since they're specifically hired to mimic someone.
The other points you mention all boil down to being ethically wrong because it's easy, which doesn't really make any sense IMO. why is a thing ethically wrong just because it's easy, if it wasn't ethically wrong when it was hard?
Would you consider a person using a voice-changer to mimic ethically wrong?