Definitely sarcasm. 

When was the last time you saw "potheads" roaming the downtown causing problems with local businesses, tourists, and patrons? Never

When was the last time someone got stoned and went home and beat their wife? Cite me an example please, and I'll cite 100 examples of a drunk doing the same.

When was the last time someone smoked too many marijuanas, overdosed, and died? Never

Folks with critical thinking skills can see that marijuana, used moderately and responsibly, pose close to zero risk. And like alcohol, when you make it legal and regulated, it makes it harder to get believe it or not.