How to talk to anti-cannabis folks

I just saw an exchange between a friend of mine, and an anti-pot person who was making some comments under a picture of a guy wearing a t-shirt that said "marijuana is safer than alcohol"

When this guy saw the picture of the guy wearing the safer shirt, he said "NO IT'S NOT!"

I copied and pasted the exchange below:

• ██████ ██████████ NO IT'S NOT!

  10 hours ago via mobile · Like · 1
• ███ █████ how so, ██████? Please elaborate, it terms of proven toxicity. Thanks!

  10 hours ago · Like
• ██████ ██████████ Just screws up your brain I think, killing cells.

  10 hours ago via mobile · Edited · Like · 1
• ███ █████ but more so than alcohol?

  10 hours ago · Like
• ██████ ██████████ Probably not but still does damage.

  10 hours ago via mobile · Like · 1
• ███ █████ not advocating MJ with this statement; simply stating it is SAFER than a legal, toxic substance. and thanks much for replying!!

  10 hours ago · Edited · Unlike · 3
• 
  So there it is,