If it is off by default, nobody will enable it and it will render some important stats useless. The RBI stats for example are our major source of information about "actual" weapon balance and we don't want to lose that.
IMHO DCC's stats are too extensive, they show when you played etc. - IMHO that should not be available to the public. In case of the RBI stats, I think I'll remove the single-match stats as I don't need them and as they could raise the same privacy issue.
If such a feature is "opt out", stats would still be "useful" but players can easily opt out of the tracking.
But actually, you're confusing two things - stats and tracking. With stats, you can't track when someone played, from which you can infer where he's from, on which days he had "special occasions" like birthdays etc. if he plays less than usual. With highscores, you still can't infer that, but you can find out who plays more and who plays less. With DCC's tracking, however, I think you can find out too much about someone. DCC should at least remove the graphs from his stats page, like the playing time of the day graph.