I don't think it's immoral, but who in their right mind takes Elon seriously? Would you really accept 1 billion dollar from a known attention-seeker scammer, if you tattoo your forehead? No thanks.
If this were coming from Jeff, or even a drug lord, I would probably be ok with it, as long as they are serious and without childish conditions.
I think you misunderstood, if Elon were to be taken seriously I would definitely accept it, but are you really sure he will go though the deal? That guy is a clown, can't be trusted a bit.