A good historian will use the fact that he can't divorce himself from his own viewpoint as a reminder to be extremely cautious. A bad one will use it as an excuse to indulge his particular biases.
And a very bad one will pretend that he is being value-neutral and objective, and show no attentiveness to the interpretative nature of his work.
And a very bad one will pretend that he is being value-neutral and objective, and show no attentiveness to the interpretative nature of his work.