It's rude to need for companion or vendor but it's also rude to group kick if you didn't set expectations for loot rules up front. New players may not understand the expectations that vet MMO players have for looting and throwing a kick tantrum doesn't really do much to change that.
Now if someone is just being a ninjabutt after rules are established, kick and ignore away.
That being said a Companion Need button is a great idea. Rank above greed but below player need.