You are describing hang gliders.
People don't have the necessary power to weight ratios to support bird-like flight, but by taking advantage of thermals flights can last for hours.
You don't need ultra-strong materials, just a lightweight rigid frame and a sail-cloth.
For stability the "wings" should be above the center of gravity of the person.
As humans, the advantage is to have removable wings so that you don't have the burden of carrying their weight when they are not in use.
Re: crippled wings, each bit of functional loss would reduce the flying ability by a corresponding amount until you simply reach a point that flight is no longer worth the effort and or not possible.
It obvious that you could in theory design a built-in hang gliders made of bones and an thin webbed skin membrane as the material requirements are well within the capabilities of flesh and blood. It would not be as convenient as an artificial hang-glider though. Only a small percentage of the population ever does hang-gliding, so it is hard to image a large majority of the population undergoing the genetic alterations needed to grow a biologic hang-glider. We do not have the genetic understanding sufficient to create biological hand-gliders today though.