To interdict missiles that would otherwise be fired at our ships.

I'm going to assume you believe that's a...good thing?

It's not a legal thing, that's for certain. The U.S. doesn't have any right to just board and search any vessel it wants out in international waters. And unless I'm mistaken, there's no law that prohibits someone from owning or transporting missiles in international waters like that, so I'm not sure on what authority we would "interdict" them.

Generally speaking, when the US decides to blatantly violate international law, whether it's a "good thing" or not depends on whether the benefits of doing it are outweighed by the consequences of doing it. The US arrogating itself the right to board foreign-flag vessels and seize their lawful cargo is going to ruffle a lot of our allies' feathers.

Seriously, who cares? We have every right to defend ourselves in international waters.

We do, certainly. But that doesn't give us the right to board cargo ships that aren't actually attacking us. If we were to declare war against Yemen and institute a blockade, we would have the right to do that....but we're not in that situation.