“’Would the Cubans be justified in shelling the base?’
‘Yes.’”
Would we be in the wrong to defend it?
Yes. When the host country wants you out you leave, even if the host country is Cuba. We defy them because we can and because we want to destabilize the Cuban regime. That doesn't change the basic principle though. If they tried to evict us, using every reasonable method short of force first, and if we forcefully resisted, would any other country anywhere support us?