Taking apart the Modern Synthesis

I'm embarked on a quest to come up with the briefest-possible account of why mutation plus natural selection can't be the primary mechanism of evolution. Here's my latest attempt:

  1. The great majority of mutations are harmful*. Without natural selection, in every generation harmful mutations predominate, and generation after generation will accumulate, leading to increased disorder and eventual extinction.
  2. Now introduce natural selection. An efficiency for natural selection of 1% may be assumed.* A 1% reduction in harmful mutations still leaves the great majority harmful (eg a reduction from 90% to 89%). For natural selection to drive evolution by favoring occasional beneficial mutations over harmful ones it would have to be close to 100% efficient, and for that by common consent you’d have to invoke the supernatural.
    *from Evolution: The Modern Synthesis by Julian Huxley.

I'd welcome rebuttals.