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.
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,
Outside of math you also need the relevant evidence, i.e., observations, which requires you to trust that they have been accurately reported.
-- Mark Friedenbach
Of course, with the prompting to state my own thoughts, I simply had to go and start typing them out. The following contains obvious traces of my own political leanings and philosophy (in short summary: if "Cthulhu only swims left", then I AM CTHULHU... at least until someone explains to me what a Great Old One is doing out of R'lyeh and in West Coast-flavored American politics), but those traces should be taken as evidence of what I believe rather than statements about it.
Because what I was actually trying to talk about, is rationality in politics. Because in fact, while it is hard, while it is spiders, all the normal techniques work on it. There is only one real Cardinal Sin of Attempting to be Rational in Politics, and it is the following argument, stated in generic form that I might capture it from the ether and bury it: "You only believe what you believe for political reasons!" 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.
Now, on to the ranting! The following are more-or-less a semi-random collection of tips I vomited out for trying to deal with politics rationally. I hope they help. This is a Discussion post because Mark said that might be a good idea.