Do squirrel monkeys make good pets?

No. Monkeys in general don't really make good pets. They require a highly diverse, fresh diet, they're messy as heck (they throw anything and everything- food, toys, poo, other body fluids- yuck....), and need pretty much constant interaction. It's like having a very strong, very needy, very messy 3 year old with big teeth. They're really not for everyone.