He begins with an argument for redundancy in such a general sense that it's almost a truism. One way or another, since you don't know for certain that your code works, you should add code (ie checks) to make sure that it does.

BUT, that general argument, in and of itself, doesn't say testing or strong-typing or asserts whatever is the answer. It seems to me that what is needed is checks that are highly tuned to the situation at hand. Just as simple unit tests are limited, Strong typing is limited to catching a small portion of bugs. I want a language in which I can add only verifications that I need, when I need them and skip the rest. I've never tried it myself but the automatic typing of some functional languages seems like the appropriate next step (and I'm currently programming in a strongly-typed language that is generally a pain in that way).