I would posit that is because many more people have had a taste of broccoli than of heroin.

You would posit based on what? Defunct rats-pressing-pleasure-button studies?

Many people have had "heroin" in the form of morphine in the hospital. They don’t turn into morphine-seekers.

Addiction and pleasure seeking is more complex than having a taste and then being hooked forever. Of course many people can't get out of this Skinner Box type of mindset.