I think that the problem with objectivity in history is similar to the problem of objectivity in journalism. Everyone agrees that objectivity is the aim, but it has also been shown that objectivity is not technically possible. So what do we do with this paradox? One response is to celebrate the inability to be fully objective by not even trying. If we can’t achieve the goal, then why make the effort? The other response is to say, well, we may never be perfect, but that won’t stop us from trying! What we would desire from our journalists is that they strive for objectivity, in full knowledge of the fact that it is technically impossible to ever be fully objective. I would argue that the same effort makes a good historian.
Bias is not directly the opposite of objectivity. But a bias is a hindrance to objectivity. If it is a known bias, then it is good to acknowledge it up front. If it is an unconscious bias, well, then you’ll have to wait for your readers to point it out to you. But to indulge your biases to their fullest is to abandon any pretense of writing history (or journalism). Instead, you are simply writing polemic (or a polemical editorial, if you are a journalist). It may be historical polemic, but it remains polemic. Yellow journalism was deplorable, and “yellow” historicism would be equally so.
So no, I don’t believe that a bias is a good thing for a historian to have. It may be inevitable, but it is not good. Affecting a posture of neutrality is no more desirable (emphasis on the word affecting).