Every clause you wrote is a confession, not an argument.
"The Social Security money hundreds of millions paid in." There is no such money. There is no account, no vault, no fund with your name on it. What was taken from workers was spent the moment it arrived, handed to the prior generation, the structure of a Ponzi scheme run by law. Musk is not raiding a pile of savings. He is naming a fraud you mistake for a nest egg.
"The trillion he stole." Name the theft. Whose property did he take, by what act, from what victim? You can't, because he stole nothing. He built rockets that land, cars an industry swore were impossible, and satellites that reach where wires never did. Every dollar came from a human being who chose to trade for what Musk made. That is the precise opposite of theft. The man who creates value and trades it freely is the one moral actor in your entire post.
"Paid no tax on." A man does not owe society a cut of his existence as the price of being allowed to produce. His wealth is not a loan from the public. It is the recorded fact of how much value he gave to others who wanted it.
Look at what you've done here. You took the words "stole" and "entitled" and aimed them at the one man in the exchange who took nothing and earned everything, while defending a system that seizes from every worker by force. You inverted it completely. The producer is your thief. The coercion is your justice.
That inversion is not an error of economics. It is a confession of values. You look at a man of enormous achievement and your first instinct is to brand him a criminal and strip him bare. The achievement is the thing you cannot allow.
You are not seeking justice. You are seeking a victim worthy of the name, and you chose the one man who made more for others than you will ever grasp.
A better question is 'Why the fuck does Elon Musk think he is entitled to the Social Security money that hundreds of millions of Americans paid in?'
As to the trillion he stole and paid no tax on.
Make him pay his tax.