Monkeys are biologically, anatomically, and physiologically very similar to humans and thus are used in research extensively to benefit us all.
You don't want to see that or know about it. Like war, research is an essential evil that is best not flaunted before the general public lest their naive comfortable eyes be repulsed.
Monkeys as pets are incredibly stupid and dangerous. If you invite this disaster in upon yourself then know that they will rip your face and genitals off first when they get mad, so anytime you see a faceless genital-less idiot you'll know what happened to them.