To be fair, it wasn't actually Malcolm's fault

First of all, it's still murder and it's still breaking and entering. You are never allowed to end someone else's life. Malcolm wasn't obligated to Vincent as an adult, since he wasn't his patient anymore. Years had passed from when Vincent was little all the way to the night that Malcolm received a plaque from the mayor. Vincent was Malcolm's patient when he was a child, and he just kept Malcolm guessing. He was free to tell Dr. Malcolm Crowe anything; including the fact that he saw the dead clear as day and they were hounding him. If he was worried that Malcolm wouldn't believe him and would have him committed that's a risk he had to take but as a child, he wasn't willing to take that risk and that's the reason that he never told Malcolm about the troubles that were haunting him [pun definitely intended], then his parents divorced, he moved away, and he was now a grown man scratched and banged up from all of the ghosts in his path and the years taking his sanity he took his anger out on Malcolm and blamed him for it even though Malcolm didn't know that he failed Vincent. He didn't know that Vincent could see and hear the dead. When Malcolm listened to the tapes he recorded from Vincent's sessions, Malcolm mentions that when he was a kid he threw up chili cheese fries all over a nurse once, and Vincent starts laughing then he mentions he's going to leave the room briefly he does, he comes back in after a few seconds and he says, "God it's cold in here," And Vincent is now crying and Malcolm asks him why Vincent is crying; but Vincent wouldn't tell him and he wouldn't tell him why Malcolm was suddenly freezing cold either; it's the yo no quiero morier scene; it wasn't til years and years later after meeting Cole, reviewing the cases and comparing them and listening to the cassette did Malcolm hear the ghost on tape and realize Vincent had the same curse Cole did seeing ghosts and dead people: AFTER MALCOLM WAS ALREADY DEAD!

Meanwhile, there's Cole. Cole took the chance and was brave enough to tell Malcolm that he saw dead people. Unlike Vincent. Vincent never told Dr. Malcolm Crowe what was wrong so Malcolm thought he had only trouble coping with his parents' divorce. But Vincent was free to tell Malcolm about the dead people in his life, but he never did and it's not his fault either since this was when he was a child and probably externally confused and scared and it was when Dr. Crowe was still living. If he had, what would happen? He would have been in better shape; or driven insane anyways from the overwhelming deeds and misdeeds of the dead!