Carol, from Emma's post "Under the law of a blockade, intercepting a vessel COULD apply globally so long as a ship is bound for a "belligerent" territory, some legal experts argue"

Most or all of those on board were intensely partisan against the Israelis. They were also clearly expecting trouble, or why the life jackets? They were witness to terrifying violence. I do not find their testimony reliable.

Remember that Israelis have stopped ships on many previous occasions, and stopped other vessels that night.
All without violence.
It is possible to abseil with a weapon in hand. I suspect that the soldiers were not expecting a fight and sought not to appear provacative, otherwise I simply can not believe that Israeli commandos could be so readily overcome by people armed only with clubs.