Ok, but also true is, practically every killer be it a mass killer or otherwise ate bread or a bread product regularly.
It's just not that simple. I'd also be willing to bet all the killers also wore shoes regularly. The fact that one can co-relate things does not mean A causes B 100% of the time, or even, that A causes B, at all.
EVERY case is an individual, and general tendencies don't mean much, if anything, useful. Look at the millions of people who use marijuana or any other drugs, legal or not, and who kill NO ONE.
And always remember that "more likely" does NOT mean "will happen".
Really?
Unless you have diabetes eating bread does not present as a mental illness. Same for wearing shoes and all those other perfectly legal activities. And while the vast majority of people wear shoes and eat bread only a small minority of the population consume drugs illegally. So I am not sure what your strawmen are good for?
The co-relation between crime and drug use is well beyond contestation. If you like I can bomb you with peer reviewed studies, facts and figures to show this. I really don't mind. This isn't a general tendency it is a simple fact.
Besides which you are looking at this the wrong way. This has to do with the fact that a small population (drug users) are responsible for nearly every murder in the country. Therefore if you want to reduce the number of murders you simply reduce the number of illegal drug users.