As a materialist, physicalist, darwinist it seems to me that the question you ask regarding 'purpose' seems unintelligible, because the evolutionist states, Dawkins states, that evolution is due to purposeless changes, undirected in nature.Dawkins makes clear that these processes a blind, pitiless, and pointless. So as a devotee of Dawkins your question seemss senseless. If all is matter and energy, and there is no timeless, transcendent purposeful God, even if the question could approach logic from an atheist, why would it matter if there is, or is not, a purpose.
The reflex for the materialist to put the question of abiogenesis apart from the quesitons of the metaphysical belief in evolution is a preemptive attempt to avoid the hard question. Abiogeneis, which science has repeatedly disproved as possible, is the supreme problem for the materialist darwinist, and one which they know is inexplicable in a physicialist worldview, thus the attempt to innoculate themselves from having to address that elephant in the darwinian discussion room.
In a discussion of semantics, where words have specific meanings it is important to maintain the distinctions for the discussion to be coherent.
Can the argument against atheism not tolerate maintaining those distinctions?