Well, who wouldn't want to see their favourite characters on screen? It's not about bias or impartiality, it's about putting forward a good reason to include the character. His argument's not bad at all.
Not when most of his arguments have been countered before many times. Like this...
"If Bruce encountered a young man who is lost much in the same way he was (orphaned, alone) he would also have a second chance to save that young boy who's parents died in the alley all those years ago."
Really?? Would he? The path he chose for himself hasn't exactly led Bruce to a happy place, has it? Why would he want to expose a kid to that? When you have a second chance, do you do things in a very similar way again? No. He did not become Batman to save himself. He became Batman to help Gotham in a way that his father could not, but he doesn't consider himself or his life desirable or redeeming. He knows the ugly part of his work, the bad consequences adn the questionable methods.
If Batman wanted this kid to be saved, he would try to let him become something similar to Harvey, or his own father. A true hero.
"he will see the potential that this boy would have if not properly looked after. He would see that there is a need to channel and harness that rage. It would be a second chance to save someone who has lost everything- much in the way he couldn't save Harvey."
Wait... does this mean that if Bruce could have saved Dent's life and sanity, he would have trained him into becoming his vigilante side-kick? What a way to save people! Yeah, great way to save an underage, give him an inferior training and have him fight against bigger, stronger and more dangerous criminals, without getting killed or killing others...

The way to harness rage it's never to enable him to get into dangerous, violent situations. If you can teach this kid to train his anger and thirst for vengeance with training, then you can also give him the necessary therapy without making him a junior vigilante. If you can keep dangerous transgressors locked, you can keep a minor in control. And being a kid it's never a reason for not being put in control, especially to one as pragmatic as Batman. It's hard, but it's better than compromising the kids life (as well a number of other things) in a life vigilantism.
Do you want a Robin that works? Have Bruce meet him when he's about 12-13 and train him (with a bunch of other teachers) for no less than 5 years (until he's an adult) before he goes into any kind of fighting. That would be, at least, somewhat realistic.