You can't have the cat owner shirk all responsibility, depending on the situation. Sure, if a neighbor's dog escapes and attacks your cat, then that neighbor is 100% at fault. However, if you know that there are dogs roaming around freely a lot of the time, even though it is those dogs' owners' responsibility to control them, you are just as much to blame if you let your cat outside and something bad happens. I'm not saying that you have to live with that scenario, nor am I saying that the dog owner is any less to blame, but at that point you do have a responsibility to your cat to not let it outside until you have found a way to deal with the dog problem.Sorry to burst your bubble, but if your dog gets out and goes onto someone else's property, it is your responsibility, and yours alone.It is your responsibility to keep your dog under control to prevent it from killing other people's pets at all times, the only exception being when other people's pets enter your yard.
Your argument holds up ONLY if the cat is caught by your dog in your yard.
If you think the owner of the cat is to blame if their cat gets killed by your dog outside your yard, it is your responsibility if your dog gets killed by the cat owner outside your yard, too.