Someday, Adafruit or other respected individuals might discontinue the supplies of the Library Functions.
Someday Arduino might discontinue the supply of the Arduino IDE. Is that a reason not to use the function because we don't learn to use the registers? With the same arguments you can force the abandonment of the compiler and tell people to hand code the machine language bytes.
If Adafruit discontinues the supply of the library there are thousands of other developers out there that might take the maintainer job for it. As long as we have the source code I don't see any reason not to use a library that is doing what it should.
One question at you GolamMostafa: Are you using Windows or MacOS X? What if Microsoft discontiues the supply of Windows or Apple discontinues the supply of MacOS X? Do you see why your sentence is definitely wrong?