Guy D - you're spot on there. The only thing I'd add is -
The Captain is untimately responsible for the safety of his a/c and his passengers - granted, and with that in mind: I think he failed to ensure the safety of either by going against ATC instructions.
Other than TCAS, as soon as he decided to manoeuvre away from where ATC needed him to go, he had no way to know if he was going to plough into another a/c.