Calling people out on stuff is argumentative, so I don't do it as much as I used to. I have just found after 42 years, that people don't change their mind when you argue with them, so why bother? Occasionally, it is necessary, when you must do so in order to uphold a high personal value. Calling out Holocaust denial might be a good example of that.
What Komp said, too, really reveals alot about the desire to prove others wrong. If you are right, you are right. When you need to put others in their place for being "not right" it usually has more to do with personal insecurity (and ignorance of one's own ignorance) than any lofty ideal.
The Rev