But the relevant question is whether audiences in the 40s and 50s would have laughed also. One hears stories of people running from the cinema crying and even vomiting upon seeing footage of the Hindenburg disaster screened.
You must understand the major flaw in this argument is the fact that documentary or news footage certainly has no similarity or comparison to a "gag" in a film. If we laughed at this scene its because a) we see little in the way of graphic detail; b) it looked typically surreal and finally, as again stated in the next reply, c) we reasonably understand that it is not real. I'm not sure if you're trying to insult the intelligence of our grandparents, but I'm pretty sure they could tell the difference. I'm almost certain I have seen just as many graphic encounters, though differently executed, in some of the classic war films as well as gangster flicks of the Golden Age of Film. Older generations were by no means "innocent and clean-cut" despite how we may depict them nowadays...
"I've seen it. It's rubbish." -- Marvin the Paranoid Android