The truth? Especially in anything related to alcohol/substance abuse, there most often is no objective "truth", as there are a lot of religious / moralizing standpoints involved. Alcoholics Anonymous, for example, has been shown to be more morals than science: https://www.theatlantic.com/magazine/archive/2015/04/the-irr...
What does help however is "housing first": https://www.samhsa.gov/homelessness-programs-resources/hpr-r...
Kinda makes sense, given that many people on the streets basically self-medicate either existing untreated mental health problems or the (enormous) stress that comes with living on the streets.