I gotta agree with you. If a monarch cannot (or will not) intervene when the long-term survival of the nation is at stake, then there is no purpose for having that monarch.
In the British system, the Monarch can only intervene in very specific circumstances. They don't apply in the cases being talked about here. Parliament had the legal right to pass abortion laws - it's not a constitutional issue and the Queen could not withhold the Royal Assent. And the idea that Muslims have taken over Britain is abject nonsense. There are enclaves in the UK where Muslims are a majority, and they have more influence than I'd like, but they are not even close to having taken over.