[fvold]

It's ostensibly "pure science", where we "just" gain more information on how the most fundamental building blocks of reality work.

It's hard to predict what new technology can come of this. For example, who could have predicted the transistor?

I think the information gained is valuable in itself, but way smarter people than me will be looking way harder at it, and suddenly a real-world marketable application pops out. If we could predict it happening, that would be the pop.

Also, don't underestimate the massive amounts of learning being done in engineering just by designing experiments and building/maintaining accelerators. That, alone, might be worth it.

[bmitc]

Those are fairly general sentiments that apply to a lot of things, though. However, funding is not infinite, and CERN has received a lot of funding over the years.