Why modern synthesis can't work

Writing on a friend's blog I came up with the following very simple account of why the modern synthesis couldn't work. I repeat it here.

Genetic mutation involves damage to genes. Damage to genes, left unrepaired, will impair a species’ performance, and as that damage accumulates generation by generation it will eventually lead to extinction. A species that repairs all damage to its genes will do better than one that doesn’t. And sure enough a very efficient gene-mutation repair process has evolved.

Now suppose someone points out it’s theoretically possible for damage to a gene to very occasionally result in an improvement, and that occasional improvements like that will offset all the harm the rest of the damage has caused, and that’s what drives evolution.

Crazy, right? But that’s exactly the basis of the modern synthesis. It’s what all evolutionists believe. It’s given as the mechanism of evolution in the National Academy of Science 80-page book for teachers, arrived at by a committee of 14 eminent experts. I've clocked 6000 visits to a page on this site making that argument and only this week had a reply--thanks Dan--and he gives me qualified support.