"They clearly weren't in their right minds."
You are of course correct. However, that is not necessarily the result of the mind-altering substances. The pattern of miscalculation and escalation throughout this tragedy also fits known sociopathic behavioural traits. The constant raising of the stakes when facing diminishing returns, ever greater risk taking in order to hide a dishonest act, is a common occurrence in certain personality profiles.
The total lack of regard for professional, moral and legal standards displayed by this skipper is a telltale sign, as is his de facto criminal attitude towards the safety of all those aboard.
I'm willing to bet that learning about his dealings with close associates will make for some very interesting reading indeed. But, for that reason, I think it unlikely we ever will.
IMHO