I don't know that it's fair to assume that the company's customer service as a whole is taking a nosedive because of what a small percentage of people are complaining about on social media. There were likely plenty of situations like this "back in the day" -- it's just that no one heard about them because news didn't travel so far, so fast. If this had happened in the early 1980s (and I'm sure it did), the OP would have gone home, told his family or a few friends, and that would have been that.
I agree that the OP "just wanted a picture with mickey", but no matter what you're wanting, it still has to happen within Disney's framework. Was the CM rude and inappropriate? If they responded exactly as the OP said (and the response hasn't gotten ruder in the telling), then yes. But if the CM had been as kind and sweet as could be and STILL hadn't let the OP get in line at that point, would that have changed anything, or would the OP feel that they still should have gotten their photo?
People here on this board exhaustively plan their trips to WDW so that they can get those photos with Mickey and great parade seats and short lines and a-list rides. Sure, it would be great if you could just walk up to a character who was wandering freely throughout the park and take photos without having to worry about getting there within a certain window or whatever. But the internet, social media, union regulations, safety standards, and a dozen other things are unfortunately working against you.
If OP truly believed that he was wronged in what happened, he should write to Disney and voice his disappointment. No one here can change policies at WDW or work to make character greetings less regimented.