"I can't be responsible for your happiness."
No, you can't. But you also can choose to not justify every cut with that phrase. Everybody has their reasons. Everybody has stuff. Everybody has..well, everybody does.
But using that as a fulcrum to be mean, to be unkind, to be cutting? Not everyone does that. My unhappiness usually stems from someone being mean, being unkind, being cutting. Doing that, and saying that you're not responsible for my reaction to it, is...well, it's...something.