Big data aggregation makes this process much much easier. We are living in unprecedented times of mass surveillance, and we have yet to have a real reckoning of what that means in the hands of extreme ideologies.

Also things don't have to be as extreme as literally killing all members of a minority group for this to be deemed "bad". It can be as simple as targetted influence campaigns to push certain policies/agenda. The ability to influence on mass scales has never been easier and cheaper. There are many examples throughout the world of how that influence has been used. And while yes influence campaigns have always existed in some form, the degree of targeting and the ease at which this has been made is a case where and difference in scale is a difference in kind. This is a powerful tool that I don't believe anyone should have access to. States, companies, or individuals

I've heard that countries that kept better records of their population had more Jews captured by invading Nazis than those countries that had worse records. I don't seem to be able to find hard evidence for that though, so maybe it's not true.

Still, I think it's clear that data can very quickly go from harmless to harmful depending on who gets their hands on it. The Nazis absolutely did have a problem finding all the Jews they wanted to kill, and abundantly available data about the religious preferences of literally every citizen being immediately available to them would absolutely have caused much more death than already happened.

Thanks to big data you can do it in a very subtle way. For instance, you can call people for vaccination programme, that will make people from your list of undesirables infertile. This way you won't even have to build concentration camps and you can claim "oopsie daisy it was a bad batch, our bad" etc.

That's a more extreme example, but there are lot of other ways creative government could make the lives of people they don't like miserable or impossible.