No offense, but I'd probably done the same, maybe with telling you in front why and if you'd not change the vote would come.
Pushing some DPS as a heal is nice and all but first and foremost you should not let the tank go without a heal, just throw it at him to let him know you are there, never mind the fact that he may not need it at all.
If I'd want a third dps look-a-like on a healer slot, I'd look for a game like that...
People these days might be rude, for kicking you without saying anything, BUT you are somewht rude too for not healing a tank when he drops to 25%, those poor fragile things get scared a lot, you know? Never heard of a WoW-Paladin using Bubble and Hearthstone? (For those who might not know -> google

)
Anyway, if you want to continue that way, at least let your party know beforehand, even if its just a "Yo, i'm healing if it's necessary don't be afraid, but mainly i'll push dat damage!".
Just my two cents
