I'm pretty sure that the minimum security would have to be provided, but let's talk about another aspect first. Every year thousands of people are boarding their yachts to visit some tropical islands like the Seychelles (near a popular somali pirate fishing area
) and live to tell the tale. Nothing happens. And in most cases they have no hired guards or anything like that. Those pirate hits and abductions that you're talking about aren't that common.
That said, there are many ways of making the platforms secure, starting from installing a radar and a sonar to monitor the traffic around the seastead and ending with automated water canons able to sink a boat if needed. Of course, if you're expecting a whole invasion of some third worlders armed with RPGs, not many things are able to stop it, but French Polynesia is inviting tourists every year, and most of them are rich for pirate standards. Are they being abducted or robbed at gunpoint? Not really, if you trust the reports.
I entirely agree with your data. Nevertheless, you must understand that such a seastead/ micro-nation is a new, innovative and disruptive entity on the global horizon. Several minds are going to be perturbed, and a few of them might even drift toward some decisive action.
When I say 'pirates' the image that immediately comes to mind is the impoverished Somali pirates. But, anybody operating outside a national setup is a 'pirate'. Consider the legendary pirates of the sailing ship, colonial era!
In fact, that very same seastead/ micro-nation, on account of its disruption of the world order, would be considered a pirate of sorts. Such an outlook toward the seastead would attract buccaneering mindsets currently serving in various national Navies to plot their own disruptions.
When that occurs, they would be no Somali pirates, but mostly indistinguishable from standard Navymen, as most if not all of them will be erstwhile Naval personnel drawn from various national Navies, now come together for this lucrative mercenary op for what to them seems like some noble action to save the world order against a borderline 'pirate' state.
If you think this is far-fetched, read the rosters of mercenary ops in Africa, where the governments of whole countries have been rudely overthrown, because of the lucrative mineral wealth. The pretext: poor integration with, and attempt to disrupt, the global order, exactly what an upstart seastead would be accused of. The subtext: lucrative riches on offer, whether in Africa, or on a seastead.
These ops would be full-fledged invasions, using the latest naval weaponry 'borrowed' from 'somewhereland'. Does the seastead/ micro-nation have the stomach to even contemplate such an eventuality of overwhelming warfare, let alone plot counter measures?