I generally never enter an online debate with the intention of convincing the other person of my point of view. I enter a debate to provide a (hopefully) strong counter argument for the benefit of the lurkers reading.

As an example, I am extremely unlikely to convince a tankie that the USSR's authoritarianism is a bad thing, but my arguments may help a less politically savy reader not become duped by a tankie's propaganda, and that's worthwhile to try for.