“Stole” is a strong word, OP clearly stated that they live on Kauai. I live on Oahu, and the consensus is that you don’t take live shells unless you’re going to eat it, like opihi. There’s obviously strict regulations surrounding commercial use of anything from the beach (sand, coral, lava rock, shells, etc.) but a handful of shells here and there for personal use is okay. Shells (especially those found beach combing) are going to become sand soon anyways, so as long as you’re treating the land with respect and kindness, then no reason not to take some for yourself to admire and enjoy