I suspect this would've made him really look like the true psycho he is, and remove any doubts about the level of malevolence in him. As NBC did it, one is left guessing what they edited out and why, while the parts the editors wanted us to see are continuously repeated, and the all the hype for the footage has the effect of lionizing the killer as somebody special.
Granted it would have ended up being recorded an readily available all over the place (as the excerpts are now), but the whole thing would have been out there for the record.
I agree...show it all or none. It does leaves questions as to what was edited out. As much as I dislike NBC, I doubt any other news organization would have chosen NOT to air it is some form or another.