If we're moving towards public healthcare, we should not legalize illicit drug
You're dead wrong. He said it causes lung cancer or COPD. I said it does not for the average person.Right. He's saying people that smoke weed run the risk of contracting illnesses that put financial burdens on other taxpayers. Your retort was smoking didn't cause those things- which it certainly does.
"However, while a few small, uncontrolled studies have suggested that heavy, regular marijuana smoking could increase risk for respiratory cancers, well-designed population studies have failed to find an increased risk of lung cancer associated with marijuana use." --https://www.drugabuse.gov/publications/research-reports/marijuana/what-are-marijuanas-effects-lung-health
"Tashkin says these studies controlled for other factors including cigarette smoking and found that marijuana smoking, even among heavy users, did not seem to elevate risk for developing either COPD or lung cancer." --https://health.usnews.com/health-care/patient-advice/articles/2017-11-24/is-there-a-connection-between-copd-and-marijuana-smoking