If you want to get to the heart of the heroin problem in Florida, you only need to look at perfectly "legal" prescription drugs. These things were handed out like candy, and as a result people got hooked. Then when the state started to crack down, people who were addicted to painkillers had to go and find something to fill the void. Heroin is cheaper (somehow) and easily available, so that's where they turned. It has nothing to do with legal marijuana. People have been smoking forever, and they didn't turn to heroin then.
The legalization of marijuana is a recent event in the U.S. but the heroin epidemic has been going on for many years. So legal pot is not to blame for the heroin epidemic. It is more likely that prescription drug use leads to heroin. We see an increase in prescription pain killers that are very addictive and those users are going to look for the least expensive path to support their drug habit.
As a couple of generations of under-the-radar marijuana smokers can attest, marijuana does not lead to heroin. If a person is prone to addiction and they try marijuana first, they might end up a heroin addict, but that is the exception. Millions of baby boomers have smoked marijuana on and off since their college days, without moving to more dangerous drugs. Debbie Wasserman Schultz is just raising this issue to get votes from older Floridians in a tough reelection campaign against Tim Conova.
There are many people who would state the fact that Marijuana usage has lead to people using harder drugs such as heroin. However, this is something that can not be taken to have a solid foundation since many people have smoked Marijuana throughout their lives and have not moved on to harder drugs. Marijuana though addictive for many people must be seen as something like alcohol for many people drink alcohol but when done irresponsibly things can get out of control. Its not the marijuana that leads people to harder drugs, its simply a person's addictive nature and lack of self control that can lead a person down this path.