For me the reason is the same than with all collection of personal data on social media. There is no any one specific scenario I'm worried about per se, but it has more to do with the potential for misuse in the future. I hate to compare things to nazies but it's the best example I can come up with. Just imagine what a goldmine facebook user data would've been to them. There's always the possibility for a fascistic government of some kind to take power one day and a database containing these amounts of personal information of near every person alive has near infinite possibilities to be misused. I couldn't possibly imagines all the ways this information could be used against me but it can and thus the safest way is to prevent them from having the data in the first place. It's sort of an insurance. You hope that it will not be needed and it probably wont but going completely without is pretty irresponsible too.