Natural Selection is a metaphor because there is no actual selection going on. It took you guys a long time (many years) to admit to that!
Shows how stubborn memes are.
Darwin thought of Natural Selection as similar to artificial selection, the way a farmer selects for traits in his crops while cross breeding them. He (being an agnostic) probably had the idea of some superior intelligence doing the selection.
Talking of 'filtering' is nonsense because this automatically implies a set requirement (a sieve of sorts) based on which the Natural Selection takes place.
There is actually no set process at all that can be called Natural Selection. It is just chance which depends on local environmental conditions. A species could survive very well in one corner of the forest and get eliminated at the other corner depending on the conditions. It is pure chance and talking about it as though it is a well understood process is incorrect and dishonest. Seen along with random variations...the entire process of evolution is just chance.
Evolution is fact happens through active adaptations of organisms to environments through an internal communication within them, that causes phenotypes to change suitably. Now....you guys obviously don't like that idea because it implies some sort of an inner response and intelligence that is anathema to you.