"Or you're always choosing the right side."

The problem is that if you ever win an argument when you are wrong, subsequent arguments with anyone who has accepted your false conclusion leads to further errors. Furthermore, to avoid this, it is not enough to always choose the right side. You must be right about everything you convince your opponent of. Even the right conclusion can be supported by false evidence. Lastly, you will probably engage in arguments that have no right side or conclusion. Such arguments should not be won or lost - rather, both sides should admit when there is insufficient evidence to support either case.

Of course, you could always choose the right side, one hundred percent of the time, every time. How likely is that compared to the likelihood of being argumentatively superior, though? Having a compelling enough argument to convince someone else of a false conclusion means having a compelling enough argument to convince yourself of the same thing.

I could be wrong about this, though :)