It's counterintuitive for dogs to bark!
Historically, when they were hunting in a pack, if a dog found a squirrel and barked in excitement it would scare all the other squirrels away. The other pack members would not be happy campers!
But when man started to develop breeds to use in hunting, terriers were taught to bark so when they pinned a squirrel or other animal down in its burrow, their master could find them.
At first they wore bells on their collars, but they got caught and strangled the dogs. So they were taught to bark.
I think we need to accept that this is characteristic of the Schnauzer breed, know that Schnauzers do tend to be "barky," and not be overly sensitive when we hear it from others.
Yes, it's still rude when we hear someone say, "Oh, you have a barky Schnauzer!" Just as it would be rude for someone to say about a child, "Well, of course he's acting up, he's a boy!"
But instead of getting nastily defensive, we might use the opportunity for a little (sarcastic) education. How's this for a reply to such a comment?
"Well, of course! Schnauzer's were breed to bark to inform their masters when they pinned down their prey. But he's just a puppy now, and I'll have him trained not to bark in no time."