OK Zmann I should have worded my question a little differently. Others said that they are dangerous, and that they have seen the cab come off - also signifying dangerous. I should have opened up the question to include why people think they are dangerous and would never put them on a truck. And why are some people such as yourself so against them?
On some trucks the additional view of the frame is not that bad - on my Avalanche, the AMP Research steps totally hid the frame.
I didn't ask to compare and contrast the benefits/drawbacks to a suspension lift, or about the difficulties with a body lift such as bumpers, lines, cables, hoses, etc. The high quality kits I have used in the past addressed all of those issues - they had custom brackets to relocate everything that needed to have stress relieved or be repositioned. Not sure how many body lifts you have installed, but I've installed a total of 5 on trucks - some owned by me, and others owned by friends. In every case, the kit I used was complete with every bracket, bolt, and part needed.
I've never used a 5th wheel hitch before, so I can't really comment on that point.
The OP specifically stated he wanted a body lift, and did not want a suspension lift in any way. I just don't see what's so bad about them. Your opinion that a suspension lift is better is fine - I like suspension lifts too. Body lifts do have some advantages, like not raising the center of gravity as much as a suspension lift.
Curious why you think they are crap for ANY application.
On my Avalanche - I wanted to run 40" tires. I used a 12" Bulletproof kit for the suspension, but that alone didn't give me the clearance I wanted to run the 40's, so adding a 3" body lift was the perfect solution. To go another 3" on the suspension would have cost me thousands in custom fabrication. The body lift was about $300.
The same thing can hold true for others. The difference between a 6" and a 9" suspension can be significant in terms of cost. That extra 3" requires larger more expensive components, in addition to other issues like custom driveshafts, clocking/lowering the transfer case, custom steering components, custom shocks, etc, etc, etc. However going with a 6" suspension combined with a 3" body lift would get you to the same place for considerably less money.
Again, I just think it's a viable option in some cases, and don't see why people think it's so bad.