Sorry, Gallagher is a CS professor. How could he have graded you poorly for disagreement? I can see how that can happen in the social sciences or humanities but it isn't clear to me what that would even mean for a CS prof.
It's not as if all CS classes have to use objective standards of grading.
It's also not the case that objective standards of grading can't be gamed.
It's also, also not the case that objective standards of grading exist beyond, say, multiple-choice exams, which are more or less useless for testing practical knowledge.
Link.
Given the positive reactions, I think the professor seeded them with a positive impression of the site's content.