There are good reasons to do it correctly, at least.

Marijuana legalization isn't all good.

Legal cannabis seems likely to be much better for people/countries/states than cannabis being illegal, though there are some downsides.

See:

http://www.slate.com/articles/business/moneybox/2016/11/amer...

https://www.vox.com/2014/9/23/6218695/case-against-pot-legal...