It's tempting to interpret the Equal Weight View (EWV) as offering positive normative advice: 'when you disagree with someone you take to be an epistemic peer, you should split your credence equally between both your conclusions.' But this would lead to implausibly easy bootstrapping. (Two creationists don't become reasonable after splitting the difference between each other. It's just not true that what they (epistemically) ought to do is to give equal credence to both their unreasonable views. Rather, they ought to revise/reject their prior beliefs altogether. Cf. wide-scope oughts.) To avoid this problem, Adam Elga restates EWV merely as a constraint on perfect rationality. That is: if you fail to split your credence in this way, then you're making some rational error. But even if you satisfy the EWV constraint, you might be making some other, more egregious, error. So it doesn't follow that, all things considered, you ought to follow EWV.
Or consider Roger White's argument against imprecise credence. It shows that we're "irrational" (i.e. imperfectly rational) to have other than perfectly precise credence in any proposition. But given our cognitive limitations, I expect we'd do even worse if we tried to give a precise credence to every proposition under the sun.
The fact is, we're not ideal agents. We have no hope whatsoever of being perfectly rational. And this leads to the problem of second best. That is, attempts to conform to norms of ideal rationality may end up leading us even further away from that goal. What we really need are norms of non-ideal ("second best") rationality, that recognize that we will make rational errors, and so incorporate strategies for recovering from such errors. In other words, we need to know what to do in case we are in an irrational position to start with -- how can we revise our beliefs so as to make them less irrational? Bayesian updating and other rationality-preserving rules are no help at all when your initial belief state has no rationality to preserve.
[I'm sure this isn't an original observation. I know many moral and political philosophers are interested in non-ideal theory. I'm just less familiar with epistemology. Can any readers point me in the direction of epistemologists who work on non-ideal theory?]