Selective Service is a strawman here, because it is anything but selective in practice, applying as it does to all males (not just able bodied ones, they don't determine that until there's a draft and associated physicals).
And if that means you're against registration or conscription based on innate abilities such as intelligence, then aren't we in agreement? After all, Luke's strength and steelhard skin are a) just as much a part of him now as Tony's brain is a part of him and b) less potentially dangerous. So, if we're not going to require Tony to register his brain, we shouldn't expect Luke to register his powers.