but i just haven't learned how to be human yet

Yes. Obviously. He characterizes these fans as self-absorbed, socially deficient, intellectually incurious, emotionally dependent on formula, and “excruciatingly boring.” That is not neutral description. It is a negative judgment about their character and the way they live.

2. Does Ebert imply that a depth of knowledge about a fannish subject is inherently bad on its own?

Not quite. His stated objection is to people using expertise as a display of devotion, a source of status, or a substitute for broader interests and spontaneous social interaction.

I would argue that the rest of the review makes his position a little more clear, though.

3. Does Ebert state that this pattern of behavior is a quality of all fans?

No. He says “a lot of fans,” “extreme fandom,” and “such people.” He is identifying a type of fan, not making a literal universal claim.

4. Did the reader see a mildly critical opinion containing the word ‘fandom’ and immediately succumb to an emotional reaction rather than fully read and engage with the passage?

Calling people socially inept, intellectually empty, self-absorbed, and excruciatingly boring is not “mildly critical.” It is openly contemptuous.

A person can understand the passage perfectly well and still object to it. Disagreement is not evidence of failed reading comprehension, no matter how many condescending bullet points one wraps around the accusation.

5. Did the reader see the words ‘socially inept’ and immediately assume this refers solely to autistic people? Why or why not?

“Socially inept” does not mean “autistic,” and Ebert does not explicitly mention autism.

But the behaviors he associates with social deficiency overlap heavily with stereotypes about autistic people: intense specialist interests, encyclopedic knowledge, reliance on predictable conversational scripts, and difficulty improvising socially.

The word “solely” is doing dishonest work here. The relevant question is not whether the description refers exclusively to autistic people. It is whether Ebert treats traits commonly associated with autistic people as evidence that someone is socially or intellectually defective.

6. Is the job of a cultural critic to ‘let people enjoy things?’

No. Critics are allowed to criticize fandom, fan culture, consumer identity, nostalgia, and the social uses people make of art.

Readers are equally allowed to criticize the critic’s assumptions, generalizations, and contempt. “A critic’s job is not to let people enjoy things” does not mean every hostile remark made by a critic is therefore insightful.

There is also a rather important contextual omission here. Ebert did not write this as a general essay about fandom in the age of twitter, harassment campaigns, shipping discourse, or whatever present-day fandom behavior the quotation is now being aimed at.

He wrote it in his February 4, 2009 review of Fanboys, a road comedy set in 1998. So this is a late-2000s review discussing a particular stereotype of 1990s fandom. The film follows a group of friends who plan to break into Skywalker Ranch so that their terminally ill friend can see The Phantom Menace before he dies. Ebert’s argument is that the movie identifies too closely with its heroes and should have mocked them more. The rest of the review makes his position much less ambiguous. He calls their fandom “an idiotic lifestyle,” describes them as “tragically hurtling into a cultural dead end,” dismisses their knowledge as having “no purpose other than being mastered,” and ends with a joke about their mothers cleaning up after them.