Fact 1 - lots of people, maybe even most people in the western world, use alcohol to varying degrees and have jobs and families that are not falling apart due to their drug use.
Fact 2 - many currently illegal drugs are less severe in their acute effects than alcohol, are less severe in their chronic effects than alcohol and are less addictive than alcohol.
Combined, these torpedo the point stated in the article, but not your point. The only way to address your concerns there is with studies of what happens in places like Amsterdam and Colorado.
Personally I would argue that even if legalising drugs makes some things worse (more users, more addicts), applying the cost of the drug war to mitigating the harms instead of amplifying them is a win regardless.
This argument always seems a bit silly to me.
Perhaps these people oppose legalization in part because they don't want more drugs to be as common and socially acceptable as alcohol and all the evils that come with it, and simply regard alcohol and tobacco use as a largely lost cause. This argument is common and it always frames the issue as if the person is 100% pro-alcohol.