He was human and so human rules apply. I would have tried to stop her. The same way I would have tried to stop Willow from killing Warren. I don't see why Faith gets sent to prison for killing human beings but the likes of Fred and Willow are justified, no matter what the crimes of their would be victims were. We have laws and courts to deal with people.
Agreed, to a point. Willow killed Warren for murdering Tara. Human laws apply there, and Willow was wrong for taking he law into her own hands. Faith killed one person by accident, then several others while working for Wilkins. Both cases of humans killing humans in violation of human law.
Technically, Professor Seidel violated no provable human laws. There was no admissible evidence, no witnesses whose testimony would have been admitted as anything but the ramblings of a deluded person. Just try and get any District Attorney to take his case to court, or one judge who would be willing to hear it.
Seidel's crimes were beyond the reach of human law, and if he were to be stopped, human law wasn't capable of doing it. Yes, he in effect murdered students, or at least sent them to almost certain death or worse, but there was no possible way to prove it. Given those facts, the only way to make sure that he was stopped had to be what actually happened, and the one person most justified in doing so would have to be one of his victims. In other words, Fred.
What Gunn did was noble and commendable, but, in the end, destroyed his relationship with Fred much more surely than if he had allowed her to do it, then been there to support her if she needed it, which I, personally, don't think would have been the case. As I said before, I saw Fred as a lot tougher lady that most folks apparently do.