There are more realistic scenarios today: hypersonic missiles and railguns. Both can't be mitigated by any known naval defense system.

Of course they can be mitigated. Knock out the targeting or launching platforms and you break the kill chain. Plus hypersonic cruise missiles and railguns are still mostly in the research phase, and it's looking like railguns might not really be workable at all.

1. Sure once we're under way but that doesn't change how good they are from a first strike perspective.

2. As a species we can land a rocket on a barge, do you think we can't land a big crowbar on a slowly moving target?

3. Might make 2 more difficult but a 1-ton tungsten rod is pretty durable.

Certainly more potent against a static target but with modern tech and one skilled, ethically ambivalent engineer, these days you could probably hit a row boat.

Because the barge is carefully positioned to be in a place this exact rocket drops from the sky.

Satellites are not 'sitting in orbit', they are falling on earth extremely fast, and not reaching it only because they fall sideways. Since they go very fast, they have immense momentum. To attack a target you have to steer that momentum elsewhere, and that takes a lot of energy and precision,and you also have a very small attack area for every satellite. So to cover all earth reliably you'll need a constellation with numbers like Musk's Starlink - i.e. thousands of satellites.

Do you really not understand the differences in difficulty between a cooperative, planned ahead rocket landing, and an adversarial attack on an actively evading target whose position may not be precisely known even at the start of the attack?