Parents tend to be terrified of a couple of things. Being arrested, the concenquences WILL follow you for the rest of your life. Getting bad stuff ( hey they don't know) being addicted ( yes I know) associating with "bad" people and geting into "trouble", expirementing with "hard" drugs.
And of course all the propaganda that has been fed to them over the years.
Find and watch the movie "GRASS" there is a ton of GOOD information and accurate scientific information. You will also see the propaganda that affected their parents and them. Remember this lie has been repeated for over 70 years. there is a lot for them to UN-learn.
It is your job to educate them without offending them. A very tough gig
take care
Doctor G