Like Daisy, I think using "base weight" to drive decisions is kind of meaningless, too - and to some extent, so is "FSO" (from skin out) weight. All it does is quantify pain. What does have meaning is whether the stuff you're carrying is adequate to keep you warm, dry, hydrated, fed, and reasonably comfortable/safe on the trip. Anything that doesn't is just dead weight (aka "the sum of your fears.") I still tend to follow Colin Fletcher's advice: (a) if you need it, take it (b) if you take it, take the lightest functional version you can find/afford.

The guideline about the percentage of body weight you can comfortably carry is good for newcomers to the sport, and for a weight budget for a given trip. Newcomers generally like rules; they often find them reassuring (even if they're bogus.) Telling someone they can comfortably carry 40 pounds, then deducting the 15 pounds of excess body weight, gives them a very realistic 25 pound load. Then you can work with them to get rid of half the stuff they thought was necessary for a two-night weekend (one of which is within a mile of the car.) They'll still find the remaining 25 pounds heavy, but they'll have the reassurance of a Rule: "They" say I'll be fine with this load, so it must not be too heavy."

Having said that, I do watch my pack weight closely: my total weight, not my base weight. For a normal two or three night trip, I can take a pot and a cup; for a longer trip, with more food and clothing, I might reduce the kitchen to the cup. I also set a much lower budget for myself than the "usual" 25%; at my age (70), I tell myself that by managing my pack weight (and my expectations about mileage, terrain, and length of trip) I can extend the number of years I can still backpack using all of my original parts (knees, hips, etc., are still going strong.)

But mostly, Fletcher is still right: if you need it, take it and accept the fact that you have to carry it - or figure out an alternative.