I think a more accurate way of saying it would be:
Your brother technically made the choice that led to his own death. However, there is a good chance he would have not made that choice had the State not grouped marijuana in with meth, pcp, coke, heroin, etc., which are at least tens of thousands of times more dangerous, and mushrooms and acid, which are hundreds of times more dangerous. In truth, cigarettes and alcohol are thousands of times more dangerous. Why doesn't the State provide accurate statistics of addiction potential, long-term health effects, likelihood of overdose (defined as death or organ damage during use, or maybe anything requiring medical treatment excluding shooting people tripping with thorazine, which has been shown to be more likely to cause a bad experience than letting the hallucinogen or entheogen wear off), etc.? There's a lot of conjecture about that, but there is some info from NORML and a lot of academic study of Prohibition and its conjectured, eventual effects on our drug policy.
Accurate information could well have saved your brother's life---we don't know---but if we had a study with a sort of "control group" (though it wouldn't be a blind study), comparing two similar countries where pot is treated differently (there's arguably at least one, the Netherlands, maybe two if you include Mexico), and see what happens, we could give some loose statistics about the likelihood that your brother would still be here.
I am sorry for your loss as well. You can probably indirectly blame the State, but we can only surmise what could have happened, sadly.
[Note to future employers scouring the web for dirty secrets: having an opinion on the drug policy doesn't mean I do drugs---perhaps I just care about how the State treats so many people I have read stories about in the paper.]