It sounds like they are very passionate about their faith so they want to share it with others. But they are on another mission than what they really should be on, so it`s very controversial.
If this is really the case, then I find it rather disgusting due to the lack of respect for Afghan people, the breach of the codes/rules they're meant to abide by and the potential implications for all the international peacekeeping forces on the ground (not just US). On the other hand, further information and an inquest would seem appropriate to really assess whether it's proselytism or a case of strong faith distorted. This also raises an issue re the training military forces abroad receive, particularly when on "peacekeeping" roles. Non-interference is probably one of the most difficult lessons to learn when dealing with a different culture especially if under extreme circumstances. It isn't surprising either that attachment to faith and /or own values deepens in "closed communities" within a so-perceived hostile/alien environment, in which case the healthiest solution might be to ship them back and provide counselling. To be followed by improving cultural, linguistic and psychological skills training for the future; or thinking twice before sending out troops abroad.