Absolutely correct and for the reasons given in my post#563 which you did not copy:
So all that could take over a whole population is a largely beneficial mutation. Problem with that is for any new feature, for any new function, indeed for any new gene you would need a multiplicity of mutations. These are not all going to occur at once. Since neutral and slightly beneficial mutations will die off very quickly and only spread to very few individuals, this accumulation of mutations is impossible and therefore evolution is impossible.
One beneficial mutation is not impossible though highly unlikely as you yourself admit. However several beneficial mutations, all of them working towards the same goal, occurring at random is totally impossible. Just one would constitute a miracle. The millions of them that would have been necessary to account for all the diverse features of the millions of species alive right now as well as the progress from bacteria to human is utterly impossible that is why the only rational explanation is intelligent design.
Only if you ignore these factors:
There is a lot of DNA, sometimes called "junk" DNA. Although that name overstates the case, it is not generally expressed (read as a protein). Mutations there (and pre-existing oddities) will not generally express themselves, but such coding can do so if the right "start reading DNA code here" sequence is added.
For a given base pair, it is not always a case of, virtually everyone has, say, a "G" here, and any of the other 3 letters is a mutation. A given percent of people will have some other base pair, and as long as people don't have offspring with their siblings, that's rarely a problem even for "hamrful" mutations.
In the same way that a very short piece of computer code can call up a big subroutine and perform a complex function, a single base-pair mutation can cause a big difference in an organism's structure. While the fruit fly example where an extra pair of legs or wings pops up with a single mutation is not a useful feature, that doesn't mean that no such mutation could be helpful, given how many will occur.
Viruses can transfer larger pieces of DNA to radically different parts of ones chromosomes, and even between species. Large expressed sequences are not apt to be helpful, but some will.