Natural select certainly has a component of luck in it in terms of the individual, and yes the bulk of the sperm (both good and bad) are killed before reaching the egg. But only sperm with good mobility generally ever reach the sperm ... thus a screening process ... the next screening process is "can the sperm enter the egg" ... and then can the sperm fertilise the egg ... and finally can the combination of chromosomes grow from an embryo to a child. Thus natural selection is more apparent when you consider the sperm population (???) as a whole rather than an individual sperm. The better quality sperm are more likely to result in a child.

You are only considering outside appearance. The "inside" counts too!!! It is possible that a sperm can look good on the outside and swim well but can not fertilise an egg ... thus why ICSI is not 100% successful ... it is not even close to 100%. We still have much to learn about human Reproduction.
that is the reason why to me whether it is ICSI, IVF of IUI, it is not natural selection because the sperms that would otherwise be killed are still used, those that had to take the "perilous journey" to test out their "fitness" didn't. Thus I don't think IVF allow "more natural selection" to take place than any of the other methods.... It is just giving all the sperms an equal chance of fertilising the egg (which is very different to natural selection)...

While no miscroscope would give you a clear genetic screen to all sperms, the bulk of the "bad sperms" do get screened out by observing their physical characteristics. Even in natural conception aka natural selection, it is not foolproof against chromosome abnormality. that is the reason why 5 in 6 pregnancies (in natural conception) ends in early miscarrriage (and this has nothing to do with the mother's womb or what she did!)

Yes I have been thinking about donating our embies... though I think we have to serious discuss about it first. I have also thought about donating my eggs. But time is ticking for me and by the time we try for #2 and #3 I think I might pass the age cut off.