Not really. If healers doing less damage results in them having no raid value, then the only value that healers presently provide is linked their damage output. I wouldn't agree with that viewpoint personally.

If your point was that "such a percentage increase to tank damage could not mathematically occur through reducing healer damage output alone", then that's probably a more sensible way to phrase it rather than talking rubbish about healers doing negative damage. It's fair to ask for clarification when someone types out an incoherent response.