Hi Syamasu:
What's your question? I certainly agree with John inre natural selection not requiring variation (although I would probably drop the reproduction part simply because ns refers to survival, while "survival until reproduction" relates more to how we define fitness - but that's just a quibble), and evolution requiring variation (note the distinction). Selection pressures on a population or species can be purely abiotic as I think I mentioned in the other thread where Peter, you and I discussed this). Selection pressures can also be biotic but not related to competition (disease, changes in food availability, habitat destruction, etc). Cheetahs as a species, for example, are highly susceptible to diseases like feline encephalitis because they're pretty genetically uniform. The ivory-billed woodpecker of the southern US is probably extinct, primarily because the old growth dead trees where it nested have been pretty much eliminated. The local population of my namesake, the quetzal, in Area Protegida El Arenal near Matagalpa in Nicaragua has gone extinct for much the same reason (elimination of both food trees - wild avocado - and nesting trees - balsa).
I'm afraid that what John has posted is pretty much mainstream - with nothing to argue about. How is what he posted supposed to "change our opinions"?
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