In Islam, burial at sea is about the worst way to go - only accepted if, while at sea, the body would be subject to significant decay before proper (albeit hasty) burial on land could be arranged. Since they were on a seriously large ship (aircraft carrier IIRC?) "respectful" would have been stick him in a freezer in the morgue until next docking.
Overboard was to mitigate any squabbles about what to do with him upon landfall. Done, gone, nobody knows where.
However, if that ceremony at sea could be taken as an insult, that doesn't make me unhappy.
It's just that my skepticism and distrust of all things flowing from the obama outhouse, I mean White House, keeps me from accepting all things bin Laden as officially presented.
That we gave up some secret stealth tech to "get him" adds to my skepticism.