There is no getting outside of the fact that you, a human being, are interpreting the past through the subjective lens of you, a human being. If one is trying to be honest and careful, and not simply fall into a trap of writing about what one wants to see, one has to proceed somewhat carefully. You need to be self-aware and make sure to introduce some self-skepticism. I occasionally say, "well, maybe I should look a little deeper here, and make sure that what I think is going on is really true, or look at it from a different angle," and so on. Occasionally I do find that my initial assumptions don't really hold if I subject them to any real scrutiny, and thus must revise them.

(The fact that we are worried about how other colleagues will receive our work can play a role in this desire for self-revision: we know that a sloppy argument will be criticized as sloppy, and we don't want that to happen. This fear of other scholars is trained into one as a graduate student, when many of your classes are nothing but mercilessly sitting around and nit-picking the work of other scholars. In my view, we are trained to be very pedantic critics, and rarely to be generous readers, and I do think that can hobble people, since it is easy to be a nit-picker and hard to be a builder of something new.)

There are times when one is faced with many possible interpretations of the past given the evidence, and the evidence cannot distinguish between competing interpretations cleanly. In such a cases it is fine, I think, to announce this, and to announce why one has a preference for one version of the story over another. The reader is left to make their own decision, and no one has put over any pretense about objectivity whatsoever.

Lastly, at some level it ought not to matter that much. No single book or article is ever going to be the "last story" on any historical episode. In scholarship in general, there is not meant to be any dogma or any scripture. Everything is a constant state of revision and argument. If one historian makes a strong argument for X, and it is plainly motivated by pre-held ideas, then so what? It gives me an opportunity to make a strong case for Y, which might be motivated by my own pre-held ideas. The rest of the community can sort through the various books and arguments, and perhaps a synthesis of Z will emerge, or perhaps everyone will discover X is more plausible than Y, or vice versa, etc. Scholarship is a communal form of knowledge, not an individual form of it. It is right and well that strongly opposing views are built up and put out there, and then criticized, dissected, synthesized. That is pretty much the only model we have for growing knowledge that seems to have reliably worked over time.

All that being said, we do have norms and expectations in our community, and people who blatantly are driven by purely ideological/partisan/etc. considerations, and commit scholarly fraud like misquoting, deliberate omission, lying, etc., are considered hacks. So you can go to far in such things — consider the case of, say, David Irving or Dinesh D'Souza, who are considered just blatant frauds by any historian worth talking to. This is because they go so far with their bias that their works are unreliable lies, not worth considering. There can be many different versions of history, and many different motivations for doing it, but if a given scholar is not trying to make an intellectually honest argument, then they will be considered a hack. And yes — to head off any bright questioners out there — the decision of who is or isn't a hack is itself, of course, a subjective one. But what isn't, in this model of knowledge?