That sentence came immediately after several criticisms of specific behaviors and tactics that could plausibly cause one to not get taken seriously. So the term "people like ESR" in this paragraph could be inferred to mean "people who behave like ESR". In fact, he even starts out "I see ESR as a epitome of [certain attitudes and behaviors]".

For example, because of his past behavior I do have trouble taking him, personally, seriously. But I would not use that as a formal argument against any of his specific ideas "ESR believes X, ESR is a Y, therefore X is false".