My first camera was my mothers Brownie (Holiday?). I was probably 5 or 6, and didn't have a problem loading 127 film.
However, there were probably a lot of people that did have problems (or never tried because of perceived difficulty, impatience, etc.) that were suddenly taking pictures when the Instamatic came out.
Think of it this way, how many of us would be on APUG if it were back in the days of text-only computer interfaces. No mouse, no clicking, no graphcs - just text and commands for everything.
Personally, I'd not find it difficult, but I work in IT and deal regularly with people who can barely figure out email.
I still can't get my mother to understand that Google is a web site, and Firefox is a "browser" that lets her go to websites. She thinks they are one in the same, which makes trouble-shooting difficult when she tells me Google won't open. (Because of this, I made about:blank her home page.) Oddly, she knows the difference between the TV and a TV channel.
The Instamatic brought photography to many people who probably would not have even tried.