However as Marcus Aurelius, a Roman philosopher-emperor once said, "A scowling look is altogether unnatural; when it is often assumed, the result is that all comeliness dies away, and at last is so completely extinguished that it cannot be again lighted up at all. Try to conclude from this very fact that it is contrary to reason."
If you can't say something without raising your voice, then you're not trying hard enough. Stop going through the motions and start being cognizant of how you come across to people. Ask yourself whether you are building, or simply maintaining or God forbid destroying. Being forceful, determined, and assertive isn't the same as being mean.