It most certainly is an opinion, and it was first published by him in Feb 2009. You do not seem to be able to understand what an opinion is, if you continue to confuse his opinion as a factual basis for your own opinion.
What other basis do you have to support your own stated opinion?
I give you a list of the top schools, and the fact that none of them have anything listed on their pages concerning writing headlines, and that is all you have in response?
Universally agreed to by whom? No one recognized as a leader in the journalism industry seems to agree to it.
So, NBC News should not be taken seriously, since they have a headline on their homepage right now that reads, "Al Qaeda bomb master wounded in drone strike?"
Likewise, CBS News should not be taken seriously, since they have several headlines on their homepage right now that read, "Powering the Future: Power from wind or waves: Why pick?" and "Future of TV?" and "Honeybee crisis: What's killing the bees?" and "Fake mountain: How did illegal construction go up?"
I don't think that you should discount these major media outlets just because they choose to use headlines with question marks. It's a tactic to get people to read the article, and while we can both agree that it is a less than ideal one (in our opinions), we can't agree that it is universally accepted when there is no supporting proof of that statement.
You are right on one thing - it's not up to debate anymore. You are unable to formulate any factually-based response.