Sorry but you're missing the point. Yes, dogs have been bred to serve different purposes and that this impacts the dogs themselves as far as their personality and abilities. However, discrimination against specific breeds is a stand-in for discrimination against the people who own them. Again, I would just point right back to that dog whistle.

However, there is a point that can be made here on genetics which is that even for a professional, visually identifying a dog's breed can be very difficult. My dog is half corgi and half mini poodle but regularly is misidentified a cairn terrier. If she were to bite someone and it was reported, it's pretty reasonable to expect that there'd be a report about a cairn terrier biting someone - even though she's not one.

There are also indications that a dog's breed only accounts for a very small amount of its behavior (source): "In particular, the researchers found that aggressiveness — how easily a dog is provoked by things that are frightening or uncomfortable — is almost completely uninformed by breed."

It is easy to draw similarities between discrimination against breeds of dog that is built on a foundation of bias and ignorance, and discrimination against people that is built on a foundation of bias and ignorance.