Knight - people aren't only put in prison/jail (glad to say I really don't understand the distinction) to protect society, there is also a punitive aspect. He wantonly took from women that which satisfied his desires and still shows no understanding that they weren't put on this earth for his benefit.
In addition, if you haven't ever been a caregiver or spent time in nursing homes, assisted livings, or other places where somewhat addled elderly men live, you might be shocked at how grabby and sexually inappropriate many of them are. Many of these men were sexually mild-mannered before slight cognitive losses set in, and Cosby was far from mild-mannered in that arena.
Also, 81? pffft.... I've been aggressively propositioned by centenarians!
He did the crime it's time for him to do the time. There are - and should be - consequences for his actions.
p.s. He is spending money. On lawyers. Oodles of it.