This is just my opinion but after everthing that has happened, Cullen knows that most mages will not go back to the circle willingly. I believe that he doesn't want the mages to see the Templars as jailers, but guardians. I believe that Cullen still has a bit of the ideal view he had when he was a child, and he wants the Order to be seen the same way.
The problem is I don't believe the bulk of the order agrees with him. Thats why I see this a more for himself then for the greater good.
While I know Cullen left the Templars, does leaving them really mean you are no longer a Templar?
Personally, I don't think he idealizes the Order anymore. I think he used to, circa DA2, but he seems to have lost his rose colored glasses. I like to think that it has to do with the breaking of the Nevarran Accord and changes within the Order itself, but alas, it seems we'll never know what really happened between DA2 and DA:I. Is he still a templar? Technically, no. It is my belief that he'll always be a templar at heart and care about it's basic function in keeping Thedas safe... but DA:I doesn't seem to think so. So... meh.
As for what the Order should be moving forward, I think he's seen all the things it can be, good and bad, and realizes that while there continues to be a need for the templars in some form, their form and function need to change. Also, the geopolitical landscape is vastly different than it was. No one knows whether or not there will be Circles or whether there even exists an independent Templar Order after DA:I. But he only gets a couple of sentences to talk about it without any details.
As for why this means it's "more for himself than for the greater good," I think we're having a miscommunication, because I don't understand what you mean by this sentence at all. I think he has an opinion about how things can change. Whether or not the templars agree with him seems immaterial, since it's no longer his job to make those changes.
edit for top: my inspiration of the week! 

http://feylen.tumblr...st/120399951717