That's kind of how all military alliances work though. Even the ones currently in place. Alliances revolve around mutual military help. Sometimes that means you get dragged into wars that are not of national interest or all that beneficial in the short term to a country in question.
A very pragmatic approach and it would be reasonable if applied to "alliances" such as economic, social, political or any other form other than military.
In military alliances, people die. Countries are laid waste. There is genuine human suffering on an unbelievable scale.
This far transcends any other form of alliance.
A military alliance can be useful for the security of smaller nations but those countries must weigh the obligations against the benefits and should always (in my opinion) only embark upon them in such a way as to ensure the defence of their own homeland.
In the case of Europe, it is a continent that has been at war with itself for centuries. We have seen the rise and fall of Empires. France and Germany at war with each other almost constantly. Holland attempting to build an empire of its own. Spain.... Denmark... the Eastern European states scrapping for control of the Balkans. Blimey, we can go all the way back to the Roman Empire, or the Greek wars of antiquity.
The British have been to war with just about all of them at some point.
No continent has engaged in war to the extent that Europe has.
The EU grew out of the darkness of World War II and has eradicated war between its member states. This has led to an outbreak of peace since 1945 the like of which this continent has never known. There is no intention of any member state going to war with another.
But others, on the outside, are not so peaceful in their intent. The big bear to the East still looks at Europe as a place to be conquered.
Britain doesn't need a military alliance that will drag it into wars in places the offer no threat to us and don't seek to harm us. What we need is a force of sufficient size and capability to deter those nations that might think of trying their luck.
That's my idea of a military alliance. One of mutual states with mutual interests and no external agenda beyond the security of its own borders.
A threat to one EU nation is a threat to them all because no other country is interested in invading, say, Poland only. An invasion of Poland would only be the start of an intended continent-wide assault and therefore would be a direct, real and present threat to the UK mainland.
Britain's current involvement with NATO works against us because it is completely US dominated and subjects member states to American interests, which are not necessarily to do with ours.
Britain was only needed by the USA in Afghanistan and Iraq for political reasons..... another permanent Security Council member siding with them to give political legitimacy to wars that were completely illegal. Nothing more than revenge for 11/9. There was never the slightest threat to the British (or US, come to that) homeland.
I would rather we declared neutrality than be a part of any military alliance at all, but that's not a popular opinion here in a country that is psychologically still living the world wars of the 20th century. I'm very much in the minority, but that's my opinion for what it's worth.
But hey....... Brexit. Shall we get back to that..?