5.100 Marijuana leads to heroin? Nearly all heroin addicts have used marijuana sometime in their lives. So, some argue that marijuana should be illegal because marijuana users are likely to become heroin addicts. Use a Venn diagram to illustrate the fallacy of this argument by sketching sets for M = marijuana use and H = heroin use such that P1M•H2 is close to 1 but P1H•M2 is close to 0.