The head of the Colorado PD's office actually told us at an informational meeting that they view working for the DA as a huge black mark. While he didn't say it would be an automatic disqualification, he did state that there was no PD he knew that could even consider being a prosecutor.
That's just nuts. In my old office in Texas, we had a number of former prosecutors in our office. For two years, I interviewed law students from every law school in the state at the UT Public Interest Law Conference for internships in our office. Trust me when I say that having volunteered or worked at a prosecutor's office was NOT a black mark. It was a plus. Anything that illustrated an interest in criminal law was a plus. The fact is that public defender jobs are not easy to get, especially right out of law school. It is much more feasible to get a prosecutor's job coming straight out of law school--at least it was in Texas, where very few counties even have public defender offices. Also, one of the best, if not THE best way to get criminal trial experience right out of the gate is to go work for a prosecutor's office. That kind of experience, even if it's on the side of the prosecution, is incredibly valuable to a public defender. In my experience as a public defender, I have known plenty of PDs who could never imagine being a prosecutor. Personally, I tend to fall on that side of things, although it's not something I would ever completely rule out. But, the idea that working for a prosecutor should disqualify you from being a public defender is simply ludicrous. A good lawyer is a good lawyer. And if that good lawyer can bring the passion and professionalism to representing the indigent accused that she brought to representing the state, then the indigent accused are better off. That's the way I see it.