I think the whole concept of point streaks as opposed to kill streaks may already be a means to solve this. If proper reward points are already in place for capturing flags, defending flags, even 3 flag domination bonuses, then the overall reward will be hitting your point streak benefits that much faster.
I am guessing that kills themselves may be lower point value in these objective based games. In TDM where the kill is the objective then the point streak rewards are generated off the kills, headshots and assists solely. In Dom, HQ, Demo, Sab, S&D or CTF where the more important goal is the objective, it makes more game sense to go for the capture. If a capture is worth 5 kills in point comparison, you will see people being objective first as it gets them that much closer to a streak reward.
As for the whole k/d ratio arguement, I personally never cared about the stat. But I can see the frustration when you are trying to win the match and you have teammates who are ignoring the objective in attempt to pad a meaningless stat. I'll gladly go 10-20 with 3 captures and 10 defends if it means winning the match 200-0. If an opponent thinks he played a better game because he went 40-10 with no captures or defends then that is simply laughable.