Your argument makes sense as long as you consider something “private” if it’s shared with Facebook itself.
If you consider something so “private” that you would be upset that an algorithm on a secure serve might use it to target an ad to you - after you read and agreed to exactly that behavior when signing up - perhaps you shouldn’t have given it to them in the first place. At what point do you take personal responsibility for giving away this information you consider to be so private and valuable?