I'd go so far as to say that integrity of state is a requirement to build robust software. If your state is ill-defined, it's pretty much impossible to write software that behaves correctly.

Sure, you can guard against some forms of bad data and fix it as it comes in (or abort with errors if your system can handle that), but in order to do anything interesting, you need to make assumptions about the data. the only operation you can perform without assumptions is the identity function, and most software requires much more than that.