Healthcare is a scarce resource like anything else. There is a finite number of doctor-hours, drugs, supplies, etc.
Price is typically the mechanism used to allocate scarce resources.
If there is no price, then people have no incentive to not over-consume.

Like dude said, when you don't have to even think about price you have no concerns at all about seeing a medical provider. So every concern you have will be check out. Even unnecessary things. You'll be going to the dermatologist to get a benign, but unsightly, discoloration taken care of. You will go to the doctor when you have a simple cold.

There has to be something that makes people have skin in the game, which is what co-pays and deductibles do. If there is no cost sharing, then there has to be rationing. And I think that would be much much worse