The red court and Fomor certainly don't do anything useful for winter and they were still members of the Accords.
A unilateral position of hostility towards anything strong enough to influence their operations is an untenable position for the fey to take.
They're one of the biggest fish allowed to cross into the mortal world, but they can't fight the whole world at once while doing their job at the gates.
The behavior you're describing is also directly the duty of summer to prevent. Since the courts aren't actively at war now I think we can assume the he.
I feel like there's some sort of fundamental disconnect between what I think I am saying and what people are responding to that I am not sure how to either correct or respond to. "A unilateral position of hostility towards anything strong enough to influence their operations" is the only stance that any nation state in the history of ever has taken. It's like everyone ever operates. In all reality. Like, how is this even a question? Only it's a bit more complex of course. Because you have to qualify hostility, and you have to quality anything and finally you have to qualify "strong enough to influence their operations".
Let me try:
1) "strong enough to influence their operations" - there are degrees here. An ability to read facebook is one thing. An ability to, through operatives in the country, attempt subversion of your nation's citizens is another. An ability to, at will, get access to any and all your secrets, is a third one. Our crown is the third one. It completely invalidates any and all measured of security, compromises all Winter's agents, and puts all Winter's short and long term operations at risk.
2) Anything - we are not anything. We are a free unaffiliated agent. We can't rely on Heaven's protections even. In real life terms, there's a difference between a British spy ring, a Russian spy ring, and a nigerian private citizens spying on USA top secret military research.
3) Hostility - this one has to be qualified the most. Any nation state that hopes to survive long term has to protect its secrets. And protecting their existing secrets always, always takes precedence over the possiblity of getting new allies or information. That's just how the basic logic works. Secure what you have, then expand from there.
What I am saying, in more detail, is that:
1) Molly is not a part of some sort of peer power to Winter. She is, at best, an ally of a Knight of the Cross, and no, Michael wouldn't be allowed to bail her out of this mess.
2) Existence of the Crown is a security risk on par with, and, in my opinion, exceeding, that of Archive, Anduriel's shadow listening and others. Because those, if nothing else, all have an established theme and limitations (Archive - only something written down, and the information can explicitely be removed from it; Anduriel - limited amount of parallel processing, only works in real time, only works through shadows). The Crown pretty much has none. It can find lore long since removed, view ancient past and pierce any and all wards, barriers and protections.
3) Winter has secrets. Some of them are Winter's own and critical to their operations, like operations against Outsiders, short and long term projects to keep Winter going, secret of how Winter was made. Some of them are Mab's own, as Bob has shown. Some of them do not belong to Winter. Do you really think than in her thousand years in office Mab has never sworn to keep someone's secret? To do everything in her power to prevent some knowledge from spreading or to eradicate it? I am almost certain she did. And if not she, then Mother Winter. Winter has obligations, which are threatened by the mere existence of the Crown of Eyes.
4) Going back to 1, Molly is a
free agent. Unlike pretty much everyone else, she is not bound by a mantle of any kind. She is not bound by magical oaths. She is not bound by universal rules like angels, including fallen angels, are. She can do anything she wishes, burn Vatican down, break the denarii out to let the Fallen operate in the open, lie, bewitch, confuse, and trample all over free will of mortals with her Charms, and Heaven would not be allowed to intervene save sending a knight after her, because, again, she is not bound by the rules. Moreover, as I understand it, she can't be (easily) bound by magic oaths. She can promise something, and then break her word, and there would be no physical or magical backlash. If Odin swears something, he is bound to it. Archive is, if not a slave to her mantle, then heavily influenced by it. The Fallen can only act through mortals or Heaven will be allowed to correct the scales. Molly has none of those and many more restrictions. She is free to operate on Earth and in NeverNever as she wishes. Ally with anyone, and betray any and everyone as she pleases.
5) Molly has used the Crown to spy on Mab in the past and derail her plans in regards to Mab's sworn vassal. That's essentially an attack on Winter Court. Because Mab was fully in the right to go after Arawn, and, with how debts and obligations seem to at least partially be inheritable in the setting, had a claim to Lydia in at least some capacity. And if Mab learns about the Crown, she is more than smart enough to connect the dots, or at least have a strong enough suspicion to take offense and be able to act on it.
These five points paint the following situation: If Molly explain the Crown to Mab, then the situation will be as follows: There is a free agent without strong backing from any established force, whose loyalty or at least security cannot be guaranteed. This agent has a highest possible level of penetration into any and all Winter's secrets, and secrets of Winter's allies, and into secrets Winter as a whole and Mab personally might be sworn to uphold. It cannot be easily guaranteed that the agent won't leak these secrets, or will not act against Winter. There are no convenient ways to established trust with said agent, because they are not magically bound by oaths or custom. The agent might fall into enemy's hands, or might become an enemy themselves. The agent likely has already acted against Winter using this power.
Mab might not attack right there, ok. But we'll be getting a five dot Enemy: Winter background out of it. And it would probably be hidden from our charsheet for better surprise. Essentially, at the very minimum, we'd be setting ourselves up like old Nicky did in Skin Game, only worse.
I honestly can't see how anyone can believe that Mab and Winter would allow themselves to become as vulnerable as they would be when letting the Crown free, if given a choice. And there will be a choice there.
EDIT: And that's not limited to Winter. Titania would do the same. Odin, I am fairly sure, would do the same were he to learn about full power of our Crown.
Either Molly's allegience need to be guaranteed, or she needs to be taken off the board, if her Crown becomes known, and she's not strong enough that acting against her is too dangerous and resource-expensive.