Depends what you mean by infinite.
I guess what you're asking is if we run out of money, can't we just print more? I suppose money is basically a universal unit of value, so to speak: ie. instead of "this is worth two cows four chickens and a duck", "this is worth £1000". So because it is more of a concept than a physical item, we can't "run out of it" in the same way we run out of an actual physical resource.
The issue is that when you just "print more money", at what point in the chain do things go out of order? For example, Joe wants a new car so prints himself £100k. He buys his car from the dealer and he's happy. He gets bored of his job and decides to quit. Now he can drive his car all day. Joe drives too fast and gets a ticket. That doesn't matter though, he just prints £100 and off he goes. Joe realises he'll get his licence taken soon, so he decides to build a racetrack where he can drive as fast as he likes. Joe buys more cars. He's using a lot of petrol.
Now imagine everyone else starts acting like Joe.
Oil has run out, but everyone's so rich that even the last gallon of petrol is effectively worth nothing.
Manufacturers can't keep up with demand for products. Their employees are overworked. They leave. They can print a salary from their inkjet.
The bosses don't care. They just use the office photocopier.
Third world governments are swimming in just as much cash as their first world counterparts, but they don't have the resources to develop. Or the people. They're all rich too.
One person could afford to buy all the land on Earth, but who gets it? There is no highest bidder.
Soon, groups of people start to prepare for war. They use the little resources they have to build weapons, to fight for power. Now, their vast wealth is useless. They can't buy anything. If asking nicely fails, war is the only solution.
Joe watches the mob of torches from the deserted stands of his racetrack. His car sits abandoned on the grass. It doesn't seem as special anymore.
Apologies if that got a bit fantasy towards the end, but the point still stands. By making money infinite, you remove its value, and so it ceases to exist.
tl;dr: Money makes the world go round.