I think many people underestimate the effect that intoxicants (toxic substances=poisons) have on a person’s thinking. Their on-going use changes a person’s thinking, feelings and behaviours.
Imagine drinking poison every single day from the age of say, 15 through 25. Imagine the downward spiral in thinking, reasoning and decision-making. Any mood-altering substance changes a person, even the THC in cannabis or Magic Mushrooms is another example of an hallucinagen.
A substance is used to help change a mood, to get excited, to come down, to get up, to sleep, to get excited, to change perception and so on.
Add to that everything else going on during those formative years (the brain developing until age 25, understanding sexuality, video-gaming, becoming an adult and on and on) and we have a cocktail of unpredictable actions that can, and do, take place. Substance (ab)use has become so normalized that we no longer question their impact.
I absolutely believe it plays a huge factor in people’s behaviour, just as trauma, family dynamics, abuse, and the list goes on.