I think everyone is special enough that their life data warrants preserving. If archeology and history has taught us anything, is that we are curious about the daily lives of ordinary people, to be able to understand and delete to our ancestors.
I know I am curious and history books leave more questions than answers. Even the most well preserved facts about kings/dynasties/wars are partial at best and leave out so many interesting things out...
My feeling is that archeologists et al would love 10x or 1000x more data about what happened in the past -- not to have to guess everything and never be sure "is that really what happened?"
An awful lot of digging into people's past online is done for mean-spirited reasons like finding something to embarrass them.