You are truely subjective in your assesment.
He can do what ever he wishes. You may not like it but never forget he is free to do whatever he would like.

What I said was not wrong, just not what you would do. I wouldn't do it either but if he wants to, how can anybody stop him?

I haven't encouraged anything, I answered his question.
And if you use a spacer on the bb then you will have to re-adjust the front der. and then the available trave comes into play.

What you don't see is that you have no problem with your modification, (the bb spacer), but anybody else's is encouraging the abuse of their equippment.

"This is real simple.If he has a shimano 9 speed double octalink crank the 68x109.5 IS correct."
They may be the correct parts but it does not mean he has a good chain line.
How is it that you check chain line? or do you just take what the manufacturer gives you and pray that it works?

All chain widths will not work on a indexed rear cluster. But it I guess that is ok because it was your suggestion.