Concerning historical domain data, there are several vendors (e.g. Domaintools) that provide this kind of information, and domain registrar information usually

Concerning historical domain data, there are several vendors (e.g. Domaintools) that provide this kind of information, and domain registrar information usually contains the registration date for the domain, so proving it was a different site is possible. You're absolutely right though that it's highly problematic if we use automated tools to analyze this kind of data, as many people can end up in the wrong category due to either flawed analysis methods or faulty data. Again I'd say that currently the greater threat comes from private companies that will use this data to build "shady" rating systems which will affect the daily lives of many people, without giving these people a chance to verify or oppose the data being used against them.