I have no idea what you think the difference between "Healer" and "healers" is but, as a practical matter, there is none. Either way, it's insulting because it reflects the old school trinity mindset that the character's only purpose is to heal and reinforces the idea that powersets without healing, like FF and TA, are subpar.
Now, maybe you just never met any of those people but I can assure you they exist. Back on live I was once kicked from a team the minute I zoned into Steel Canyon and the leader realized I was playing a Trick Arrow defender. I don't recall if they specifically said "you're not a healer" but they certainly made it clear my lack of a heal was the reason.