Not every reason people drug test is invalid.
As in, you wouldn't fire someone for showing up sober on Monday morning because they had a glass of wine on Saturday evening.
The hard drugs that tend to have more destructive effects don't even show up on a urine drug test for much longer than 72 hours. So, while the person who only smokes weed after work in the evening is at risk of being caught by a drug test, the person who gets off on Friday, goes on a cocaine binge, and then tests clean on Tuesday or Wednesday has nothing to worry about. Which would you rather have in your employ? I'd choose the pothead over the cokehead without hesitation.
I'd quibble, though, with your statement: "... because drug users can and will steal you blind if they are addicted enough."
It is important not to lump all drug use together. There is a huge difference between marijuana use and use of heroin, or other opiates, which are extremely physically addictive and which do cause users in withdrawal to turn to crime to rob you blind for the next fix.
Alcohol addiction is also physical, and the need for alcohol by addicts craving a drink creates lots of petty crime.
Marijuana is not physically addictive, and users do not suffer from withdrawal symptoms/effects. Burglary and violent crime are just not fuelled by marijuana use in that way.
I smoke a lot of weed. Withdrawal isn't a big deal, but it is a thing. It's closer to caffeine withdrawal than alcohol/nicotine withdrawal though. Symptoms I've experienced when taking a break are typically irritability and insomnia for about a day or two. And of course cravings over the longer term which often brings me back.
Similar, if lesser, physical effects happen to those with an alcohol dependency when alcohol is suddenly cut off [2]
These things are physical, not just psychological. I'm an inveterate cannabis user, and have been since the age of 15, with a happy daily habit uniterrupted for years until I went to work in Qatar for just over a year. No cannabis was available, but I had no physical ill effects - was just grumpier and less chilled in general. Similarly, currently locked down and away from my usual habitat, I've not had a spliff for quite a few months. Again, I miss the vibe etc, but I am not in any physical pain.
[1] https://en.wikipedia.org/wiki/Opioid_withdrawal
[2] https://en.wikipedia.org/wiki/Alcohol_withdrawal_syndrome