"How Dare You"?

Last week, an "Appreciation" in The New York Times ran, lauding the life of Harriet McBride Johnson, a severely disabled woman who was also an advocate for the rights of the disabled. This paragraph caught my eye:

Ms. Johnson, an atheist, was unmoved by religious appeals to life’s sanctity. Instead, her rebuttal boiled down to a simple: How dare you? How dare you decide that certain people with limitations are nonpersons with no right to exist? How dare you presume to define “quality of life,” for me or anyone else, to set the value of a disabled life lower than yours, or to conclude that such a life lacks the potential for happiness and dignity because you cannot imagine how it could? (emphasis added).

What the writer at the Times -- lost in admiration of Ms. Johnson's fiery atheist morality -- seems to disregard is the intellectual inconsistency in her position. After all, without religion (particularly Christianity, which has at its core the protection of the weakest and most helpless), people can "dare" very well.

Without religion, one can easily decide that "certain people with limitations are nonpersons with no right to exist" simply because their existence is expensive or burdensome or even just depressing for other people. Those who don't believe in "life's sanctity" can decide very well that the value of a disabled life is, indeed, lower than that of the able-bodied -- more expensive, more inconvenient, less productive, less conducive to the "greater good" of the "greater number" -- and perhaps even worthless.

If one doesn't believe that we were created in God's image, and that we have simply somehow evolved from a series of chemical reactions first occurring in the primordial slime, than what is the inherent value of a life that may be precious to the one living it, but of little tangible apparent use to anyone else? And what exactly is the rationale for protecting it?