How many major international airports should large global metropolitan areas have?

Here’s a grammatically improved and more polished version of your sentence:

How many terminals should an airport have, depending on its size?

Would it be better to have one large “mega” airport supplemented by several smaller ones within the same metropolitan area, or two sizable, well-equipped airports, with maybe one or two very small airports for low-cost flights?

In my opinion, all airports should serve multiple purposes, including military, law enforcement, and emergency service mobilization. They should also be capable of acting as major logistics hubs when passenger demand is low. Additionally, I believe every major airport should have at least a regional or commuter rail connection, and there should be an exploration of direct rail-to-air freight operations that can accommodate 53-foot containers.

I personally believe all civillian airports should be privately managed and owned but with certain provisions for emergency and military related mobilization and deployment.