With all due respect people play the game for what ever reason they want - there is not "right" way to play ED and it's quite presumptuous to say otherwise. It's a sandbox game - for some that means amassing huge amounts of wealth; for some that means owning all the ships; for some that means becoming the most respected member of the Federation; for some that will be the most deadly (no pun) pilot out there.
As I said if it's an opt-in process, and you don't, why do you care ?
Okay, for one thing, the leaderboard is not something that I can shield myself from by turning it off. In a multplayer game it has many attack vectors, and I can still feel its consequences. Alliances will want to get their names up on the board, so if you're part of that alliance, suddenly you're playing the stats-chasing game too. When people start talking about the leaderboard in the forums, it becomes part of community and not just part of the game. Also, I could be a worthless target, and still get zapped because someone's trying to add to their kill tally.
But it's also about design and what you're providing incentives for. In a way, the leaderboard is anti-sandbox because it's telling you precisely how to play the game. If you want to be top of the combat leaderboard, you must get more kills, therefore killing is the way to play the game. If you want to be top of the mining leaderboard, you must mine to the exclusion of all else...
I'm not against people getting fame and notoriety and appearing in the newsfeeds, because I hope that Frontier are being cleverer there. The stories that will appear will be the 'interesting adventures in space' ones, that the game is really trying to push. If you're nakedly providing an incentive for per-kill gameplay, then that to me is less desirable. It's not something that needs positive reinforcement.
Also, if getting to the top of the leaderboard is the main source of prestige, then that kind of undercuts the whole newsfeed thing. It certaily pulls focus away from it, and a great idea might become a great idea, which hasn't really worked. Certainly leaderboards could come in later if the newsfeed thing isn't working, and it turns out that people aren't interested in interesting adventures in space. I would like to see how the game copes without them first though.