He's deriding the agile movement. He's saying if you don't know how to properly design software (up front), then he supposes that doing it in an iterative fashion is an acceptable alternative. The way he says it implies that he disapproves of it.

In opinions such as this it pays to remind yourself that not everyone is faced with the same challenges. For all the esteem Wirth garners, I feel (at least at that time) his work on compilers and programming language design involves challenges that are very different from the challenges that inspired Extreme Programming.