Not many pitchers throw balls on purpose in the sense they throw it way outside etc. If they just threw balls when they wanted to you'd never see a pitcher walk home the winning run in the ninth inning of a game in real life.
What happens is they can miss their spots, or have a bad call here an there. With these slider you can pound the middle of the plate an never walk anyone. You will get shelled but you are free to do so. However. If you're working the corners or keeping the ball low, you will have some get away from you. If you never give in and would rather throw down the plate on a 3 ball count, then you will be hit hard. If you work the corners you will strike out the batter more, give up more weak hits, and yes you will walk a few more. Just like real life.
As far as CPU pitchers walking us, they do. Just show discipline at the plate and you will walk.