If intelligent aliens get to our planet and have any kind of aggressive intentions no amount of spending would save us. It means they already have capabilities far beyond what we could achieve in a generation and proved them by just getting to us.

> It means they already have capabilities far beyond what we could achieve

It certainly means that they have those capabilities as pertains to travel, but it is not a given that they would have those capabilities in a military sense. Of course the argument can be made that you can convert that kind of power into a weapon, but I'd hazard to say that a haphazard conversion does not in fact impart upon you a godlike ability to ignore everything we could possibly do.

I'm definitely not arguing that this means we should increase military spending. I think that is fundamentally not a great idea for us in the first place. Instead, I am arguing that while the things you are talking about are widely used as sci-fi tropes and held as beliefs by a lot of people, I do not think they stand on their own merits.

The most deadly terrorist attack on the US used civilian passenger planes. A UFO doesn't need weapons to be massively destructive. E = 0.5 * m * v^2, and UFOs reportedly go a lot faster than a 767. And if they're too agile to shoot down, and never need to land or refuel, that's "a godlike ability to ignore everything we could possibly do".

If you can project an object to another planet in any reasonable span of time, you already have vast military capabilities against that planet. All you have to do is not decelerate.

No reason to believe the UFOs reached the Earth in a "reasonable" amount of time, though. There are many other interesting possibilities.

Logistics.

A well equipped squad of marines would still eventually succumb to a gird of barbarians unless they could resupply.

I think the magnitude of the difference between the opposing parties is a lot greater when it comes to comparing humans to an alien civilization capable of projecting some force light years away from their home in a reasonable amount of time.

It's more like neolithic man meets nuclear submarine... but worse. We have 0 tools at our disposal to fight anything that's farther away than the edge of the atmosphere. "They" can take a few decades to accelerate a really massive "civilization ending" object and slam it into us. It's not like we can go anywhere to avoid it.

Why do you assume these UFOs reached the Earth in a "reasonable" amount of time? The possibility that they were roaming the space for hundreds or even thousands of years before reaching our planet is as reasonable as any other.

Even if an alien civilization finds our planet, I don't see why that would imply we are inside their logistic operational range.