Please god no. We don't need more of this bullshit, especially not in this game. I don't need an additional incentive to play the game, nor do i need an additional reward for playing it. I remember logging in into a particular game for a while just to do the "daily missions". It destroys the fun and eats time without actually giving me anything worth the effort. And in the end you will only distract yourself from the game itself, which you should play FOR THE FUN OF IT, NOT FOR REWARDS.
Please read up on how achievements and those kind of missions effect your psyche, just so you become very clear about what you actually want. Personally i believe any gamer should know about it as it has implications on how you live your life and how happy you are. Yes, it's that big a topic.
Yeah the pvp achievement like get 5 knife kills should at least not be encouraged to pursue several times, though I can't see what damage it will do if players have some weekly achievements of some sort in both pvp and pve? As long as they are not of the sort of kill 5 enemies with a knife or as last man standing frag yourself.
I understand that you personally don't care about achievements or weekly challenges, it would be interesting if you could provide a source by linking it here if all gamers should be aware of these happiness shattering consequences, or are you simply talking about gaming addiction mechanics and that weekly challenges may have an impact on that?
I mean even if alcoholics exist, the rest of us should be allowed to enjoy a beer no?