Did you notice, that whenever you differed with someone, things never really go the way you imagined they would. You would have gone through the entire argument, and discussed it over and over again in your head. And it would have seemed so obvious then. The first word out of your mouth and you are on your own.
And moreover when you are giving a point of view, observe your audience carefully. The main question they will be airing is not - what? But why? Not, "what" is the opinion and what are its merits and demerits. Rather the focus will be on why you are taking that point of view. Sad, but true. So the next time you listen to a differing point of view in an argument, spend your time thinking about the what and try to let the why for a later date. Then look how much you will benefit and how many potential arguments will immediately peter out.
Gotta do some submissions in the next few days. Oh how I hate this!