"Granted to them for free"? The US has been paying Spain for base access since 1953. Hundreds of millions per renewal cycle in military aid, economic assistance, and direct spending. It was never free and it was never a favor. Spain negotiated compensation every time.
"Who does Spain need defending from?" Nobody, because of the security architecture my tax dollars built. That's not evidence the bases are a favor to us. That's evidence they worked. You're welcome. And if they can't be used when it matters, I won't lose any sleep if they get closed.