[@1Charak2]: And later on the US military gets involved.

It's still pretty evident that magecraft isn't just up and vanishing, it's pretty clear that element is outdated in terms of the setting's lore. Mystery does indeed exist, but it's not just going to up and vanish in this scenario.

Also Fate/requiem still exists which shoots this down from the start.

Do people riot non-stop because of nukes? No. And nukes don't have a will of their own to resist being fired. And also aren't all in one place where they could be stopped by other nukes. Again, there's pretty much no nation in the world that could [i]hope[/i] to eliminate Fusang or any Servants on it, so why not just keep a friendly relationship?

You also have to go to Fusang to summon a Servant without the Holy Grail. It's not possible to just summon them willy-nilly on your own, this specific location is unique as a result and is tied to the UN and multiple nations. If someone wanted to summon a Servant to attack a city, they'd need to...

Get to the island.
Summon the Servant.
Leave the island unnoticed.
Have the Servant agree with them and be unable to resist seals if they do not.

That isn't easy given that Fusang is set up to avoid these kinds of things happening.