Neil, Jon's trying to make this a bolt in replacement.... no welding. Done correctly, there wont be any structural issues (as far as making it weaker).
As far as making it stronger... those are valid concerns. But at the same time, modifying vehicles isn't for everyone. If you want to build your Jeep (or any vehicle) to do some serious (And fun) offroading and still drive it on the street, those are risks you have to accept. You can mitigate those risks by driving safely and remembering you're in a modified rig, not a Porsche.
On another note.... more people are modifying their vehicles these days just for fun; don't you want to protect yourself from being the "sardine can" . Lol