Well, it would be nice if humans were perfect, but they're not.
I think the data don't have to be 100% accurate in order to be valuable. In some cases the data can be purposely distorted and still be valuable, as in the case of GPS data. You can't get accurate GPS data because you'd be able to shoot down a plane with your cellphone as a guide, right?
There are ways in which data can be released with caveats, with a certain legal basis for it. You can say that people who use these data use them at their own risk, and that kind of stuff. If businesses are using those data, they too have a role in verifying the accuracy. I think it's a matter of disclosing the nature of the data and the underlying assumptions, and those who choose to use the data can do so by being informed in that way.
The census is a good example. Of course the census is not meant to represent a 100% depiction of the Canadian persona; it's there as a guide for folks to understand certain patterns. Is it still useful? Yes, it is, for sure.