[anateus]

That's a commonly raised issue, largely addressed by looking at actual pirate activity. Piracy is a high-risk endeavor which is only undertaken when you have: a lot of potential victims, with very high value cargo who don't have the incentive to defend it heavily, and easy home bases.

That's why basically all piracy in the world happens around Somalia and around the Philippines. Cargo ships pass with lots of valuable cargo which is insured, and crews that that aren't going to lay down their lives to protect containers. Only very recently has piracy gotten bad enough that shipping companies have begun placing any sort of defense or deterrents on their ships. In Somalia the pirates returned to a mostly lawless state, and in south-east asia the hundreds of islands serve as good hiding places.

There aren't any pirates off the western coast of the United States, and none of the factors describe above are in place. Even if seasteads starting containing stuff that's actually very valuable, as you mention, resident would be more motivated to protect it, nor will pirates have anywhere convenient to run to.

So, are physical attacks a threat that should be considered and protected against? Yes. Is a seastead in that location with that purpose at risk of an attack by anyone but someone with some sort of ideological point? Not for a while.