These quotes, together, form a non sequitur, that is what I am driving that. You state people are not buying the game to play “story mode” with “random people,” but then go on to later state the co-op is one of the draws, which for many people will be done with those dreaded “random people.” Then you state “not saying there’s no one who wants to play public story mode.”
I did not get the “separate story/co-op missions” from anyone but you, since based on what I have read, I could only assume you thought co-op and the story mode were different, since at one point you claimed people would not want to play story mode with the public then touted how people are buying the game for co-op, or simply contradicted yourself because in two breaths you downplay the importance of public co-op and then tout it as a selling point. It is either misinformation or contradiction, and based on the clarification you provided, it is the latter. 
Anyway, I maintain disappointment in Gearbox’s initial decision to force public co-op to be at the normal difficulty. It is not the end of the world, but I am not going to be an apologist for what is a very bizarre decision given how prevalent playing co-op with strangers is in games these days. By forcing one difficulty, you hamstring that portion of the population who does not mind playing harder difficulties with random people. I would not be surprised if this decision is reversed shortly after launch based on feedback.