I know it's kind of popular in hacker culture to claim that you can't possibly disagree or critique without being a total dick, a la Linus, but it just isn't true. It's an excuse and nothing more. If you're in surgery or under fire in a foxhole or are storming into a burning building then perhaps you don't have mental attention to modulate your tone of voice. Otherwise, act like a professional adult. It's not that hard.