No, it is not justified to negotiate with insurgents, because having a dialogue with insurgents only makes them more likely to resort to violence in order to get what they want. The insurgents will be empowered if a country as powerful as the United States gives them an audience. Terrorists should not be validated.
Most insurgents that I have ever heard about, seem to be so stuck in their beliefs. They are blinded to being rational. They do not try to understand other people's point of views of different beliefs. Until insurgents can do this, I really see no point in negotiating with them or trying to negotiate with them.