I love your post. I can't think of when these questions don't apply. "So what?" is the best. "Then?" is next. Actually not that impressed with "Who cares?", because sometimes you have to do stuff that nobody cares about. Right action cannot be determined by consensus, I think. More than once I've been obliged to stand out from a crowd because nobody else cared. I'm not a hero--just see stuff and have to act without looking around for approval. The issue may not matter to anyone else, but that doesn't mean it isn't important.
Of course, we don't operate in a vacuum and should listen to input from people we respect. But, ultimately, we have to answer to our own values and conscience, I think.
Otherwise, a brilliant post.