It does not matter if those "reasons" are signaling, privilege, hegemony, or having an invisible devil on your shoulder whispering into your bloody ear: to impugn someone else's epistemology entirely at the meta-level without saying a thing against their object-level claims is anti-epistemology.

Ignoring reasons why someone believes what they believe is not good epistemology.

It depends.

If I understand all of someone's logical arguments for believing what they believe, and I have the knowledge and processing power needed to evaluate those arguments, and I want to know whether the belief is correct, I should ignore all of the non-logical reasons why they believe what they believe. Argument screens off authority, which means it also screens off non-authority and indeed anti-authority.

If someone tells me the sun's shining, and I look outside and see the sun's shining, it doesn't matter if the person told me the sun's shining because they're trying to signal something else; it doesn't matter if they're privileged; it doesn't matter if they're a hegemon; it doesn't matter if they have an invisible devil on their ear. I can see for myself that they're correct. The process that generated the claim has been rendered utterly irrelevant.

But of course I've made some assumptions there which are routinely false: I often don't have the knowledge or processing power needed to evaluate all of someone's arguments, and sometimes don't even know the arguments for a belief. If so, it's legitimate to use what I know about the belief-generating process as a cognitive shortcut to judge the belief. And this is true frequently enough that you have a good point, too: in real life we don't have time to do a full-blown evaluation of the belief network supporting a claim, in which case the "reasons why someone believes what they believe" can be useful (even important) evidence. Whether you are correct or eli_sennesh is correct is situation-dependent.