some distinctions that haven't been explicitly made about problems with argument/discussion/debate...

there are several different areas to argue about..
1)What are the facts? (did he or did he not fire the gun)
1a) How do we interpret the facts? (was it intentional and/or justified)
2)What are your (and my) basic percepts, that is, what first principles do we accept? (is killing ever justified)
3)What should be done about the facts, if we can agree on 1) and 2).

Too often arguments go on forever about 3 when there is nothing close to agreement on 1, 1a,& 2, and arguments about 1a) and 2) often get heated as we use them to explain and justify each other, without realizing what we are doing......This is often what happens when the practice I call "throwing the dart and then drawing the bullseye" occurs......someone has an emotional/personal need to defend a position, so they ignore logic and act as if 1a) and/or 2) are obvious in order to make a point....etc...etc....

and, to enlarge on Wolfgang's point, if you engage in argument ONLY to win, with no regard for the truth, then you will likely ignore any attempts like this to explain it all to you!

"My mind is made up; don't confuse me with facts & logic."