why is this footage edited at all? why can't i watch the entire dialogue from beginning to end?
Because James O'Keefe is a liar. I mean that's really all there is to it. On ACORN, fracking, NPR, and Planned Parenthood he has been dishonest and completely wrong.
This video is no different. It is edited so that either (a) we don't get to hear O'Keefe's questions, (b) are told what questions are in post-production edits, or (c) we only get part of an answer. Out of context like this, the only thing I would say the DNC is probably doing is astroturfing, which isn't illegal.
Take the "bussing people out to Iowa" quote. Knowing O'Keefe's reputation, this could just as easily be referring to volunteers or campaign workers as it is to voters. We can't know because O'Keefe won't give us the unedited clips.