Hamish Harding was told directly by at least two experts not to go on the Titan according to this article in the Times
https://www.thetimes.co.uk/article/told-friend-hamish-damn-titan-sub-latest-2gfxtdbnw
Victor Vescovo "one of the world’s most accomplished deep sea pilots" is quoted as saying:
"Hamish asked to go to the Titanic in my submersible and that’s not something I do, plus it would cost millions of dollars. When Stockton was able to succeed in taking people down in his, Hamish became set on it,” Vescovo said.
“I talked to Hamish about it and I told him he shouldn’t get in that damn sub . . . it was only a matter of time before they [OceanGate] kill somebody. But Hamish really, really wanted to go to the Titanic and that was the only opportunity . . . now it’s ‘Damn, why didn’t I raise more fuss, should I have been more aggressive?’”
Rob McCallum, a founding partner of EYOS Expeditions and an expert in deepwater submersibles, previously led multiple dives to the Titanic using Russian Mir submersibles and ran a test programme for the film director James Cameron’s trip to Challenger Deep in 2012.
When McCallum heard that Harding was considering a $250,000 Titan passenger trip to the Titanic, he said: “I sat down with Hamish and went through things and showed him the flaws and the correspondence. I tried to show him, don’t do this.” But on Friday, June 16, Harding and his crewmates set sail from St John’s aboard the Polar Prince, a former Canadian coastguard icebreaker.
When you take this into account, it makes Hamish Harding (who had done deep dives before and knew how respected these people were) look like an absolute absolute idiot. He was told directly at least twice by eminent people.