Chris is unable to control himself. He admitted that the first go around happened simply because he was "very horny". Chris has a history of being unable to stop from touching people inappropriately, and unless the state has him on Thorazine, he'll be right back to his old ways. If he's allowed unfettered access to Barb, there's nothing to say he won't try something. Maybe not even sexual, maybe he's harbored some kind of intense rage against her as we saw in the jail letters. Maybe Barb has an "oopsy" down the stairs and poor Chris wasn't able to save her, or his magic hedgehogs told him to do it.
The worrysome aspect of this whole thing is that Chris might understand that he has an unlimited "No consequences" card he can play for anything. The deferral seems to be written as a blanket coverage, minus violent murder and violent sexual assault, but Chris could literally go down to the high school and start jacking off right in front, or going into a store and just grabbing some woman's goodies. He'll be arrested for sure, and put in another mid level hotel for awhile where he's taken care of, but at the end of the day, he just needs to throw down the Autism Card, and out he'll walk.
Indeed, Chris has proven time and again that he is wholly incapable of long term thought beyond a childish understanding of consequences.
But now he's served jail time and besides obviously preferring not being in jail...the worst that happened was a tantrum at a mental hospital and he spent most of the two years being bored.
If Chris does not think there will be consequences for his actions, his lack of inhibition can
and more importantly HAS led to him doing stupid shit. Petty Vandalism over Sonic Boom 'blue arms' was the lead-up to the macing incident (which I remain convinced was entirely Chris wanting to feel 'empowered' as a woman using mace and he tried to start shit, but when it didn't work out he decides to do it anyway and basically attacked a dude walking
away from him). He staged a campaign of petty hate mail such as the stupid glitter bomb against The End Games shop when they threw his sonichu standee shit in the trash. This extends to even self-harm lest we need to go into detail about the
two times he's tried DIY vaginoplasty.
And as you mention, Tony, Chris absolutely didn't sound like his opinion of his mother was all that great when he was locked up, outright saying he hoped she croaked so he could get the house, his 'temple'.
Barb's far from being a saint (and to be frank the biggest victims of Chris returning home are the unfortunate neighbors within Branchland Ct., I hope they never give the animals back because I'm sure the animals are happier and healthier outside of 14BC) , but all it would take is Chris deciding that 'assisting' her in terms of leaving the mortal plane for some reason, may it be the real one of finally shedding himself of her weight he's been trying to offload onto Cole for years, or some Merge bullshit, and he'll
do it. 
