"Government: You owe us money. It’s called taxes.
Me: How much do I owe?
Gov’t: You have to figure that out.
Me: I just pay what I want?
Gov’t: Oh, no we know exactly how much you owe. But you have to guess that number too.
Me: What if I get it wrong?
Gov’t: You go to prison"
Sure, your government could calculate everyone's taxes but I'm guessing those taxes would need to go up...
I guarantee you'll get a discrepancy letter.