As a general rule this is completely fine. However, sometimes being impolite and correct is desperately needed. As long as you are being impolite with great calm and forbearance.
Perhaps, but in most cases, people vastly overestimate how common that "sometimes" is, how desperately the "needed" is, and how great their own "forbearance" is. They bring this argument up as part of denying their own contribution to a conflict. It's so easy to deceive oneself about this that a better strategy is not to go there. Self-honesty about what one is actually feeling will mostly eliminate it anyhow.
