An investigative journalist would abide by some basic ethical rules like "you don't get to pick the story", "try to remove your own biases" and "you are not the story."
As someone who occasionally dabbles in citizen journalism, I'm insulted by the use of that term in connection with him if it isn't preceded by the word "cowardly."
ETA: He did a hack job on a man who showed incredible moral fortitude in suckering him into more details so he could properly alert the authorities to some egregious claims. I have no faith in his ability to present edited video in a way that conveys the true spirit of the events that are portrayed. Don't hide behind some variation of "well no outlet is totally unbiased in all cases", has O'Keefe ever not made his footage into a hack job?
See the difference?
I've been in amateur journalism, event coverage, and scripted narrative (TV/film) projects for a few years, now.
Photos, especially with captions or stories heavily implying context, are so easy to mislead as to the nature of the events being illustrated.
Video, as soon as you see a cut, it means someone didn't want you to see something. Sometimes it's because the content was below a grade worthy of showing (entertainment), sometimes because it is production related and meta to the topic or "breaks the fourth wall" (camera tests, pre-roll/slating, etc). Even for the concision needed in today's news environments, maybe just to focus in on the most relevant information (rare, these days) or what creates the most shock value, the ever-necessary "sound bite." Now, these are (mostly) valid practices that make sense. But they are mostly cut-downs for fast-paced environments.
"Investigative" pieces or documentaries go into narrative style. You're using the recordings to tell a story, make a point, drive emotional responses through character development, timely reveals, and satisfying conclusions. Well, sometimes the point is to leave you with unsatisfying conclusions. When done well, you question yourself, when done accusingly, to question certain "others." Even experienced video people can't necessarily describe "how could this sentence mean anything else?" (from someone who just heard it in a heavily implied context). They could, if given the raw footage, likely make into 40 different products, some educational, some comedy, perhaps a slow-building dramatic whodunit, anything. Also, it really is not that hard to get dialogue you want to implicate others. You invert the premise in a discussion for a moment, for example. "Ok, give me an example of something you would not be comfortable doing", then bait them along playing "devil's advocate" for a moment.
Or sometimes it really is simple to just present an entire exchange with a guy who appears to be helping smuggle underage girls over the border, but forget to mention that one tiny little detail about him calling the Attorney General about you as soon as you walked out of his office.