Most military equipment and technology is built by companies. There are contracts and laws that prevent those companies from abusing that power.
If starlink is critical US military infrastructure, then the US government needs to draft a contract with SpaceX to supply that infrastructure where it's needed, and enforce it. If (when) Elon abuses that power, then he needs to be held accountable.
SpaceX has many contracts with the US government, and is prevented, by law, from doing certain kinds of business with foreign companies. There's a limit to how far he can push things without jeopardizing that relationship.