Reasons I can think:

* Harm to the body

* Harm to the brain

* It can be expensive (sometimes disastrously)

* Opportunity costs, both of time and money

* Drugs alter your behavior, sometimes not in polite ways

* Addiction make you dependent on something outside of yourself, a literal substance.

* Many drugs leave you unable to work or operate heavy machinery (cars)

* Some addicts prioritize their drug over anything, even family or friends.

* Some addicts with steal to fund their habit.

Some people make it work, there are high functioning stoners out there, there are people who need painkillers for chronic pain. These people don’t let a drug affect their lives as negatively as the alternative.

But being a dependent addict isn’t virtuous.

Yes, there are obviously negative things about doing drugs, just as there are positives. But that doesn’t make it shameful.

No one is saying its virtuous.

I'm saying it's shameful to the degree it impacts your life.

If you're in endless pain, go for it.

If you're still functional while getting high, all the power to you.

If you can drink nightly and still operate, that's great.

But it's not a virtue, and that substance will be what you reach for in your darkest moments. Maybe that's a good thing, if it doesn't impact your life in worse ways than the alternative.