I disagree. There is absolutely nothing wrong with users saying: "I have enjoyed this use case that is currently allowed. I dislike the fact that this use case

I disagree. There is absolutely nothing wrong with users saying: "I have enjoyed this use case that is currently allowed. I dislike the fact that this use case will be going away. If it does happen, I am much less likely to use the site. I think you should reconsider your decision." Tumblr, of course, is free to disregard this feedback, but I cannot see how there is anything even slightly wrong with concerned users providing it.