I always thought that during the middle of this movie, it was the Richard Denning character that was a little more sound than the Richard Carlson one.
It was Denning who wanted to take that spear down with them in the lagoon, to the surprise of the others, but hey why not? No one knew what was down there and dangers did lurk. And when they did capture the Gill Man, it was he who logically wanted to go back to the institute right way, but had to reluctantly change his mind so that Carlson can continue to study his now rather unimportant rock samples (and of course, all that lead the Gill Manâ€™s escape and hurt and kill more people, so I say the real culprit was Richard Carlson!).