A degree doesn't mean you're somehow less susceptible to addiction. The risk of addiction shouldn't prevent anyone else from choosing what they put in their own body.
I could see this go either way. There are people who are, somehow, simply unaware of risks and not very interested in learning more. I'd expect at least some effect.
Do you have any source for the claim?
Refusing to explain, or cite, or accusing others of bad faith, those are conversation stoppers.
It is not that anything not proven beyond all doubt has to fall back to assuming a null. There is such a thing as probabilistic arguments, statistics, and bayesian-ish reasoning
Sometimes, people have reasons for making negative statements. It helps to show arguments, instead of immediately launching into bad faith accusations.
Talk about wasting a lot of energy!