Clearly, education in biology, mathematics, and the like should be factual. No one would argue with that.

Dickens actually mocks Gradgrind for this:

No little Gradgrind had ever associated a cow in a field with that famous cow with the crumpled horn who tossed the dog who worried the cat who killed the rat who ate the malt, or with that yet more famous cow who swallowed Tom Thumb: it had never heard of those celebrities, and had only been introduced to a cow as a graminivorous ruminating quadruped with several stomachs.

I would suspect another major point of contention is how much weight mathematics and biology should get relative to other subjects. (Now, Gradgrind does have the confusion, more obvious elsewhere, that classifications are important facts rather than fuzzy collections, and this is a confusion worth criticizing.)

One alternative (the alternative that Gradgrind had in mind, I think) is to omit moral education entirely. I take it Dickens' thought was that this is the sort of thing you wouldn't need if you were educating slaves in more sophisticated forms of labor, because their behavior is managed externally and they don't need to give any thought to how to live their own lives.

It's not clear to me what you mean by "moral education." Gradgrind puts a lot of effort into cultivating the "moral character" of his children (in fact, this seems to be the primary reason for his banishment of fancy). Very little effort is put into teaching them how to cultivate their own character, which is what I would take moral philosophy to mean (but even that may be too practical an interpretation of it!).