I agree. Not playing with someone because of their k/d is not only elitist, arrogant and straight-up nasty - it is also stupid. I haven't checked, but I'm sure even Kampy's k/d isn't that high, because in arena he will be playing with people around his skill level. The same goes for less experienced players. Also, k/d can be influenced by things like money spent on REQ packs (if you play warzone) and the amount of time you spend on social playlists as opposed to ranked ones. Finally, a high k/d could even be a bad thing. I remember in Halo 4, my k/d was pretty high, but it was only because I spent most of my time sneaking around the map with active camouflage, doing nothing for my team. My k/d rose, but my win rate fell. A high k/d could also be because of not playing the objective in things like CTF or Strongholds, or just straight up camping. And even if none of this applied to the situation you described, I still think the people in that party were pathetic to exclude that player because of his k/d.
(For the record, I no longer spend all my time crouching or camping while playing Halo. I can see now how silly it is to do so, and I now play the objective and play fair.)