I agree 100% with your comment about Christmas Is. During my first trip in '91 one of our group picked a fight with some coral, and just about lost his big toe. The coral went through his neoprene booties like a hot knife through butter. George Cook had told me to take some Army/Navy Store "jungle boots" with a steel shank and toe. They worked great over neoprene socks, but looked like they'd been through the wood chipper after a week.
I'd never go barefoot in Hawai'i or anywhere else. An urchin spike, coral cut or lava rock slash will ruin your day in a flash. at the very least, a pair of old tennis shoes, keens or even flipflops is better than going barefoot. I've been stung, cut, and slashed enough in my life to know enough never to step in the ocean without foot protection. I'm amazed when I see surfers go in urchin-dotted spots with nothing on their feet. They're either very lucky or have feet like tanned cowhide. Or both.
I just came back from Christmas Island last week. I wore Simms flats wading boots with side vents for draining water. The vents did not go all the way through to the inside of the boots. The fine coral sand went through the vents and filled up the interior lining with sand making them tighter and tighter each day. The end result was that I had to cut the lining out to release all the sand to make it through the trip. I did have a pair of Keens also so I could have made do. One of the guys had a pair off the new Simms sandals (kinda like Keens) that looked good. I have fished the Bahamas and find the wadable flats easy on boots compared to Christmas Island.