If they already knew the intended results it wouldn't make sense to do it. Science of this kind is like "here's something we haven't tried yet", which itself is pretty difficult to even come up with.

Also, money spend on something like this doesn't just disappear. It goes around the suppliers doing it and returns to the state eventually. Of course someone will pocket some money but when talking billions it's more of an investment in the area than a cost or even an investment in the actual collider. A used collider isn't worth that amount of money , so where'd it go? It didn't disappear. Money goes round.

It creates a lot of jobs and when looking at the entire supply chain, it feeds a hell of a lot of people, even if the scientific result is "oh well it didn't do anything at all." That way, it might be cheaper than supplying social security/basic income for that amount of people.

At the end of the day, in the grand economic scale, we're all riding on the shoulders of whoever digs out the the resources from the Earth, so we need to make these kind of very important projects to make it appear as if everyone else is actually producing anything at all. The science is just a nice side effect.

Will this do?

Off the top of my head, I can't think of any advance that didn't at some point depend on people just dicking around to see what they could see.

"What happens if we spin this stick really really fast against this other stick?"

"Cool! What happens if we put some dried moss around it?"

"That's nuts, man! Hey, I wonder what happens if we toss some of our leftovers in there?"

"C'mon over here, guys. You gotta taste this!"

At worst, a project like this keeps a lot of curious people in one place where we can make sure they don't cause harm with their explorations. At best, whole new industries are founded. Never forget that modern electronics would never have existed without Einstein and Bohr arguing over the behaviour of subatomic particles.

Say the actual construction cost is $100 billion over 10 years and operational costs are $1 billion a year. Compared to all the stupid and useless stuff we already spend money on, that's little more than pocket lint. We could extract that much from the spending of one military alliance and it would look like a rounding error. Hell, we could add one cent to the price of each litre of soft drinks, alcoholic beverages, and bottled water and have money left over.

Cars?