You’re right that Ballantyne mainly focuses on epistemic trespassing as something related to question answering rather than question posing. I think this is related to his definition of a field as “an extremely narrow set of questions”; obviously trying to answer a set of questions without any of the relevant evidence and skills (that someone who works in the field has) would be trespassing. On the other hand, asking questions you’re not qualified to answer seems a lot more benign; there’s no expectation of reliability and little expectation of responsibility.
I suppose it’s still possible to cause harm in a way that resembles epistemic trespassing by asking questions. For example, a 9/11 truther with any Twitter following could sow confusion by asking “What’s the temperature at which steel beams melt?” when a plane crash investigator would dismiss that and instead ask “What’s the temperature at which steel beams lost most of their structural integrity?” What makes these questions important is not just their relation to the relevant field(s) of expertise, but their relation to the facts: the answer to the former question is a temperature higher than that at which jet fuel burns, and the answer to the latter is of course lower than the temperature of burning jet fuel. By asking the former and not the latter, the 9/11 truther uses their ignorance to portray an event with clear causes and explanations as fraught with mystery and open questions.
It seems like a strange conclusion however to say that many people are unqualified to ask many questions (that is, questions that relate to fields they haven’t studied). Maybe it would be more accurate to say that the reason the 9/11 truther is trespassing (and not merely curious) is that they’re asking questions in front of an audience (their Twitter followers) that sees them as an expert on that sort of question. Thus, the truther is irresponsibility speaking on behalf of the crash investigators, just as Linus Pauling spoke irresponsibility on behalf of the medical establishment.
I think at least some people do, but I don’t have a good argument or evidence to support that claim. Even if your only terminal values are more traditional conceptions of utility, diversity still serves those values really well. A homogenous population is not just more boring, but also less resilient to change (and pathogens, depending on the degree of homogeneity). I think it would be shortsighted and overconfident to design an optimal, identical population since they would lack the resilience and variety of experience to maintain that optimally once any problems appeared.