I think cigarettes are a great comparison. I heard it a few years back.

When popular, a huge amount of the population used cigarettes despite growing research showing that it had a slight but consistent harmful effect. A hooked individual is unlikely to stop using even when given this evidence, as the product is addictive and gets stronger with network effects. Younger generations understood the harm better and had to avoid regular temptation to engage.

Comparisons to heroin are overblown. Nobody is losing their identity, money or life due to facebook. It's just a little bad and very addictive.