It's not that you must try to produce film to be able to be a critic of it. Is is that if you ARE, as the Drinker IS, then the fact that you also produce terrible fiction weakens your reputation as a critic.
If the Drinker appears on YouTube bemoaning certain tropes or poorly written characters AND THEN immediately turns around and publishes a weak sauce novella with the exact same problem, doesn't that somewhat weaken his argument?
The reason we don't consider's Siskel's cinematic output is because there is not any. However, in the case where there is, should we be forced to ignore it?
Someone that smokes cigarettes can tell me how dangerous they are and that I should avoid them but they would be more credible if they followed their own advice.