I have a Shepard who'd resist the idea of becoming a Spectre and working directly under the council more than ME1 allows (and two who, like yours, really dig the idea for different reasons), and I know there are plenty of Shepards out there who'd like the opportunity to send any of the other squadmates to their demise in place of Kaidan and/or Ashley. But, alas, that's not within BioWare's parameters, just like resisting Cerberus wasn't.
The game has been restricting role-playing ability from the beginning, though.
No doubt, but there will always be limits to what we can do with our characters, just like (as you pointed out in another thread) there have always been plot holes in space operas. The key to making a space opera or a game good is to make it enjoyable enough that people are inclined to overlook the limitations and the holes, instead of so annoying that people start trying to list them all.
When you end with something emotionally satisfying, shortcomings are forgiven. When you end with a big disappointment, that's when the nitpicking kicks into high gear.
Look at Joss Whedon's work: Buffy, Angel, Firefly, Dollhouse, Avengers, etc. You could drive a fleet of trucks through his plot holes, but for the most part no one wants to, because he gives you what you want. I've always finished consuming media he created wanting more of it, even though I knew it wasn't necessarily built on a foundation of sound logic.