The most compelling reason to see the Templar side came from dialogue with Meredith that you only get once you've sided with them anyway. :/
I only once really sided with the Templars - when Bethany was in the Circle. You can't be rude to the Knight-Commander when she has your baby sister. But then I switched sides during the final confrontation, to protect my sister, and also because it wasn't Orsino who blew up the Chantry.
I really liked how the Templar Order was portrayed in DA:O, btw. There were naive templars like Cullen, whose cute illusions were crushed by blood magic, there were hardcore guys like Greagoir, who was strict, but chose to save the Circle instead of annihilating it (with a little help from us), so I think he was all right. There was Ser Otto, who I simply adore, although he might have been a bit crazy, in a good way. But he was trying to protect the elves from demons. There was Ser Rylock, a bit obsessed with capturing Anders
She was probably the craziest of DA:O templars, if we don't count the possessed ones. Ser Rylien seemed like a good hearted kid too, not crazy or evil. Ser Bryant in Lothering was simply a hero. Ser Drass represents the kind of a templar who was probably forced to take his vows. Alistair was also sent to a monastery against his will, so I believe not all templars choose to join the order. And when you are forced to do something you hate, you probably won't do it very well. And if you believe deep down inside that your freedom was violated, then maybe you will imagine that your power over your charges is something you can use to make up for that, and that's how we get a power-hungry bastard templar
Like some guys in DAII.
Now add lyrium to that. DA:O had 2 examples of what lyrium does to templars who take too much of it, or use it for too long. And Alistair suggests that perhaps lyrium is not even needed to develop the templar abilities.
Thinking about this led me to a conclusion, that the Templar Order is as much a victim of the Chantry system, as the Circles. Templars are good warriors, they are great to deal with demons, abominations and mages. They could be like magical police
They could do something useful. I think their potential is being wasted at the moment on guarding teenages who just want to kiss, and blow up each other's heads. 
Looks like I got carried away from the main topic, but I think Cullen would support my vision of the future of his Order. If you've been doing something all your life, it's difficult to accept your profession is no longer needed, especially if you see how you can be of use.