If it's not arbitrary, what are the criteria for legality? If there are no set criteria (whether it's amount of deaths, addictiveness or otherwise) then isn't i

If it's not arbitrary, what are the criteria for legality? If there are no set criteria (whether it's amount of deaths, addictiveness or otherwise) then isn't it arbitrary by definition? EDIT: Regarding my comment earlier about whether or not tobacco is worse than alcohol: Looks like tobacco is actually the #1 cause of death [1] [1] http://www.csdp.org/research/1238.pdf http://www.csdp.org/research/1238.pdf