Game interface designers recognize how terrible the precision of controller sticks are and pretty much universally decide that a few undeserved kills are better than frustration from constant input failure. Because the controller would otherwise be too frustrating even the most competitive console title includes aim assist. The game might curl your projectile to the target it believes you intend to hit; it might nudge or lock your crosshairs to the target; it may do both and/or some other method. So why not just take away the gamepad since it is worse than the mouse and keyboard?"
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips