I'm not sure Gibbon's theories are taken as gospel anymore, particularly that Christianity somehow made them soft. That also doesn't jibe with the facts, how soft is a society that takes great pleasure in gladitorial games, etc, etc. And Christianity making any society soft has never been bourne out in the course of history and in the middle ages and later Christian nations were overtly violent as they are today. In the early 1940's the US considered itself a 'Christian' nation and we participated in the most brutal war in the history of mankind (that's WWII for you history buffs.)
Regardless, the most important thing to remember is that Rome's decline took nearly 400 years. During that 400 years there were plenty of good things going on and many generations of Romans that thought things were just fine.
The point is, those participating in the decline of a nation rarely have insight into its causes or the speed of it descent. In fact, they don't see it at all.
And one thing can be sure, the speed of our descent will likely be as rapid as our ascension. This is not apocolyptic thinking, this is not a doomsday predicition. Its just a matter of understanding that cultures and nations do rise and fall. We will too. Sure, there are plenty of nutbags suggesting the 'end is near' but there are also plenty of very wise and thoughtful critics of western society that see in our current (late 20th and early 21st century) culture a marked decline in the things, the glue if you will, that keeps societies intact. If anyone is interested in reading what some of these critics have to say, just let me know. But by definition, a declining society will not hear what they have to say or hear their warnings.
And also keep this distinction in mind, a society/culutre can deteriorate long before the country ceases to be a military power.
As for morals, well, what other measure is there of the health of a society? Germany in the late 30's was strong economically, militarily, politically and even academically. But they were morally bankrupt.