OP
I knew people who called themselves FFB-WSL (Frum from Birth With Slight Lapses)
They freely admit they were wild as a teenager and accept this, its not uncommon. And frankly I dont think its so terrible.
Look I know its against your Haskafa, but watching movies isnt as terrible as it sounds. Look I know many here will argue, But given the choice of watching movies or hanging out with his friends and possibly doing physical harm to himself. Which do you prefer?
I do think you need to seperate “spirtual Harm” vs actual “Physical harm” . One can easily do teshuva from Spirual harm and I know of plenty who did, however there is no teshuva from “Physical Harm”