You do actually. They need pc for arrest, they need reasonable articulable suspicion to detain, your simply confusing or conflating the two. Similarly a police officer needs jurisdiction, Israel doesn't have jurisdiction outside of the blockade or territorial waters.
To run a blockade you actually need to enter it, at anchor in international water after declaring your intent is quite literally the textbook reaction to a blockade and specifically to enter one legally.
Israel also says it's ok to run over people with tanks so maybe Israel is full of shit and you should trust third parties over the most active belligerent. FYI Hitler tried to say invading Poland for security reasons was legal, turns out no but Israel decided to quite literally pull a Hitler.
Stop cucking for authoritarians bud.