I agree. I didn't know him, but maybe he wanted the easier way out without telling anyone...Offcourse, it could also be the case that he didn't trust the medical system enough or was just misguided. Either way you can still be angry about his death (that can actually be a normal response), but at the very least pinpoint your anger to the stuff that actually matters and treat him with a bit of respect.
If you are angry about his death, you clearly liked him in a way and are mourning his death.