As Sid pointed out, there is nothing holding the top of the slide in place when retracted. Even if the slide doesn't "come out" when travelling, it definitely does move. One would never notice when driving, say over a rough set of railway tracks, as who would be looking in their mirror at the side of the camper at that time. Even if you did, if the slide only came out an inch or so, you probably wouldn't notice. But just imagine the slide coming out that inch, then slamming back into the side of the camper. Repeat that a few thousand times, and one would start to get the idea.
Rugged Brown says that he doesn't have the slide bars or even the stickers on the wall to tell him where to place them, and that is odd as his camper is just the newer version of ours. I hope that isn't just yet another "cost-saving" move by the company.
As for those who complain about them falling out, you simply are not installing them correctly. We have never had one fall out, and the roads up here really suck!
Yes, they are a bit of a pain to use, but it becomes part of the routine, and is no big deal. For us, they are another thing that gives us peace of mind while towing, kindof like having tire pressure monitors.