"he ran the ship at full speed, even when it hit"
Actually, Titanic wasn't travelling at full speed, and was simply keeping to the standard operating practice of the time - keep going until you see something.
"he was going to retire, meaning he could be forgotten in history"
See Dave Gittins' post, above. It appears unlikely that Capt. Smith was, in fact, going to retire after the voyage. He certainly wasn't forgotten in history either!
"he had iceberg warnings throughout the ill-fated trip"
Indeed, but see my first comment. Warnings were treated as such, but nothing much tended to happen until somebody saw something.
Besides which, as has been already commented on above, Capt. Smith wasn't even the Officer conning the ship when she struck the iceberg. How did he convince Murdoch and the rest of the bridge crew to join him in this alleged suicide/murder conspiracy?