When drugs are illegal, the economics of an illegal market tends to push them towards more concentrated highs. When heroin was legal people took it in pill form, which is much safer than "shooting up" but is a relatively inefficient delivery mechanism so you don't use it when the chemical gets to be really expensive per unit volume.

When alcohol was legal SOME people went for the harder stuff but beer was a lot cheaper and more common; under prohibition, whiskey was cheaper than beer. If you are selling an illegal product, your legal risk is generally proportional to the volume of product being smuggled or kept so you want to maximize the number of effective doses per unit volume. The economics thus favors high-concentration forms of whatever drug. It also favors faster, more intense highs, in that if people are going to all that risk to get something they want to be sure the payoff is proportional and can't afford to wait around for the effect. So cocaine becomes more available relative to pot, and becomes available in more concentrated and more convenient forms as technology permits (versus the old way of making tea from cocoa leaves and using it as a pick-me-up beverage)

So yes, "crack cocaine" was the result of prohibition. Yet even crack could be used responsibly - it's exactly like regular powder cocaine or caffeine in that regard. But responsible use is more likely if it's legal.

> whiskey was cheaper than beer

To be honest, whiskey is expensive only because it is a branding and social experiment that was successful, not because of the cost of manufacturing it.