Actually James Cameron built his own sub and is one of the few people who has gone down into the Marianas Trench.
He is a liberal Hollywood director, but in this case Cameron knows what he is talking about.
Cameron is well respected in the field of oceanic research and of deep-sea submersibles. I would trust his opinion over most amateurs postulating and certainly over the OceanGate CEO – may he and the 4 others RIP.