That wasn't the claim. The claim was:

It is worth being conversant and properly educated about the things that are important to you if you want to engage meaningfully with people who disagree. That means knowing the vocab, syntax, and lingo.

So I will ask again in a different way- why do you need to be familiar with Mein Kampf or even a single Hitler speech to have an engagement with someone defending Hitler? Isn't "he murdered millions of innocent people" enough? What more needs to be said there? What nuance is necessary?

Here was your example:

For example, if you hate manga / anime / Japanese character retardation like I do, it’s worth knowing the difference to tell people it’s stupid on their own terms.

Why? Why is it worth it? Why isn't "I hate what I've seen, I think it's terrible and I don't want to watch anymore" enough? Do you actually watch all anime to know why you don't like anime?

Also, don't be ableist.