Uhh, they literally do meth to get jacked up to rob the card game. Tony and them weren't doing meth or coke to do robberies, they did it clearheaded with a plan in place.
Jackie Jr is like a worse-version of Chrissy. Chrissy was just a bit older and so he got to see the real life, even though he did lean into the caricatures in mob movies a lot. Jackie Jr was never part of it, not really. Senior didn't want him in it. Meanwhile Chrissy only hears about his dad Dickie, and Tony. He's in that shit young.
So Jackie Jr gets spun up on some story by a dude that's fucked his mom, showing him how to cook, getting him ecstasy, and giving him a gun. So what does he do? He emulates this new father figure who /does/ want him in the life.
Makes perfect sense because it's not a crime thought up by criminals; not savvy criminals anyway. It's a crime thought up by a misfit with daddy issues who pisses himself when he gets adrenaline.
The only thing that would've made Jackie Jr more pathetic of a character is if he date raped Meadow. It's basically his only redeeming factor.