Defend weed. Give your best reasons for recreational use of pot, and why it might be fine to legalize.
...mention possible medicinal benefits
...bring up the negative aspects of anti-pot laws
...compare or contrast pot's benefits or harms with booze or other recreational chemicals
...quote names of famous folks who use(d) pot
...include references to the addictive qualities (or lack thereof) of pot
...refer to the use of pot for religious purposes
...list the myriad uses for hemp
Just explain the plus side for users and society, if smoking pot became legal tomorrow. What's your sales pitch?
Note: I was once told that this framing is "unfair", and that to have a true discussion, all aspects must be allowed. I disagree. If it helps, pretend you wrote a long paper defending pot, but you left most of the pages on the bus.