Earlier quoted context omitted.
Your lifestyle/spending in your 20s and 30s has little to do with your retirement lifestyle/spending. Especially if you're rasing children...
And is that an argument not to plan at all? Of course you can't pinpoint an exact figure, but it still pays off to plan even on a ballpark figure.
I did not say don't plan at all, just think about the lifestyle you may have in the future, not the one you have now.