So this rant isn't strictly about Protagonism, but I'm putting it here because I don't know where else on my site to put it. Need to Know is only legitimate when you don't fully trust the person in question. If you know they're on your side, you should tell them everything, even if they don't have a specific "need" to know any of it. And it's not just because of the gesture of trust aspect (although that alone is sufficient - it's the moral value of Truth). It is actually strategically advantageous to tell your whole force everything.
I know a lot of what I'm about to say won't apply to every situation Need to Know gets invoked in, but there are so many of them - both real and fictional - that it was inevitable. I'll try to keep this as general as possible without making it useless.
First, let's get one thing straight: the commonly-raised argument in fiction that "what if one of us gets captured" is bullshit. If they're going to be helping your cause, they already need to know at least who they're getting their orders from, so having any member of your force get captured still leads to a chain reaction that threatens to undo your whole organization.
For a positive reason, how's this: you can't predict the future, so you don't know when an operative might need a given piece of information. What if one of your operations goes south and someone winds up having to fill a role you didn't foresee? That is an extremely general and plausible situation. Or what if one of your top-level people gets taken? If they were the only person who knew certain pieces of information, that's all lost now. Not to mention the possibility that the rest of your members don't even find out about it until it's too late.
You can definitely contrive a situation where need to know among friends is valid. But most of the ones I've seen or heard of either in real life or in fiction don't qualify. I hope the next time you hear it invoked, you'll ask whether it's really wise to keep secrets from goodguys in the given situation, and if you do I'm sure you'll realize that the answer is no.