First of all, I think that people do need a video to realize that war, and in particular the Iraq war, is tragic and disturbing. It's one thing to hear that lots of civilians are mistakenly killed in the course of our military occupations, it's another thing altogether to see some of the exact circumstances in which that occurs.
Do you recall the story that broke soon after the video, regarding a house that special forces stormed on bad intel, in which various people were killed, including two women that the soldiers apparently arranged deceptively so that they could claim in their report that they were previously killed in an "honor killing?" The incident that the commanding general of SOCOM had to fork over a wad of cash and apologize for? If there had been a video of that, with black-clad soldiers going "Oh shit! I think these people were just civilians!" and then digging out their rounds from the bodies, tying them up, artfully arranging them, and discussing their cover story, how do you think that would have gone over? Instead of everyone forgetting in a few weeks, we'd still be watching the congressional hearings on CSPAN.
Regarding the guncam video, do you find the destruction of the van, and the attack on the building with missiles while apparent bystanders walk by to be equally unavoidable as the deaths of the journalists? I am a little surprised that the video didn't at least make you wonder at all about the wisdom of the RoE they were operating under. You don't have to demonize the pilots and gunners personally to find fault in the incident. The military's reports found that the crewmen did make the right call in every case, and summarily declared all 20+ men killed in the various attacks "AIF" (Anti-Iraq Forces), so you can't write everything off as a tragic mistake; it was tragic official policy.
Even if all of these things are rendered "unavoidable" by our political need for near-airtight force protection (like the dozens of unarmed civilians killed at Afghan road checkpoints), many people are not aware that they occur. If everyone knew exactly what went on in Iraq and Afghanistan, they might not support the military missions there (or future hypothetical invasions) so much; war reporting certainly had that effect during Vietnam. If no one ever gets outraged, what motivation is there to avoid these entanglements, or even to try harder to avoid civilian casualties in the conflicts we are already fighting?
I can only imagine that all the random milita members on the streets with rifles and RPGs that day didn't realize that the helicopters ~1km away were or could be targeting them. I agree that the Reuters stringers took a foolish risk, and that the initial incident is not indefensible. Maybe "AIF" ambushes are always that ridiculously nonchalant. Everything that happens afterward, though...
Also keep in mind that the only reason anyone (any American) ever cared about this incident was that it was subsequently discovered that two of the "AIF" were Reuters stringers. Imagine how many incidents there must have been where people who didn't work for a major Western news organization were creatively classified as insurgents. I'm sure that some of them weren't pointing giant telephoto lenses at the Bradley convoy down the block, and would be harder to blame for their own demises.