I ran into a user whose next badge was "Fanatic":
This clearly reveals his/her consecutive days. Should they really be displayed to everyone. They weren't visible to other users earlier; I guess there was a reason for it which has gone now?
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I see no harm in it. I feel the number of helpful flags is more private than this, and you can see that already.
You can already see when someone was last online, you can see very detailed what someone did on a day. So if you want to know, you can already mine it very easy. There is no point in hiding this.
If you don't like this, set your next badge to something else.