Dogs and cats....mmmm.

Dog's chase cats because they tend to run away. The dog has urges that, as people, we can not come close to understanding. It is easy enough to say it is prey drive, it is instinct or the dog sees it as play.

It really does come down to the fact that the dog and the wolf are one and the same animal at the end of the day. The wolf has not been domesticated, the dog has.
We like to think that different breeds exhibit different behaviours because that is how we have manipulated the genetics of the wolf. To an extent breed traits are apparent......but.....the dog is a wolf before it is a spaniel, pointer or terrier. It is a opportunist feeder - a hunter, a scavenger and a reaper.

To contain the dog's behaviour it must come into contact with cats that are secure in their territory and are not likely to flee from the dog. Have you a friend that has cats and dogs? If so taking your dog as often as possible to this environment and letting the cats stand up for themselves will work wonders - given time.
Another thing that works really well is getting a couple of kittens yourself.
Work on your Alpha status and recall and remote down at the same time as feline therapy will help.
The dog is not nasty, bad or evil. You are not a terrible person for having a dog that behaves in this way...it is doing what comes naturally.