I'll bet it was the "I never unlocked it" comment that got you kicked more than not having it equipped. Too many times I've been with a group and the titan pulls out his hammers or fist of panics something and says, "Oh crap, I didn't have defender on." The party leader was probably trying to avoid that or at least organize weapons/blessing, etc. Not even having it unlocked showed you're a new player with no commitment to your character or desire to be a helpful fire team member. No one wants that player. Go solo a nightfall or play some Rumble.