Technically, anyone can print their own money. It's only illegal if you print someone else's money (that's called counterfeiting). If I want to create a million Luke Bucks, no one will stop me. However, there's two main problems with creating your own currency:
First, it costs money to run a printer. Paper and ink aren't free.
Second, Luke Bucks aren't worth anything to anyone.
So how do I make a currency that's valuable? With guarantees and social contracts.
The US Dollar is only valuable because the US Government is a generally well respected entity that makes various guarantees about its currency (though their guarantees say very little directly about the value of the dollar). Pretty much everyone inside the USA does business using the dollar. So, we have a social contract that your dollar will be worth something at your nearest grocery store.
I can offer my own guarantees and get people to use Luke Bucks. This is exactly what cryptocurrencies do. The token would just be funny money if not for the network of people and software that power it.
With the addition of smart contracts, anyone can create their own money printer (a token contract) without needing to create a new network. Put your guarantees in code and print your own money. You can even let other people use your money printer with whatever rules and restrictions you want.
This is exactly what we're doing with the Koinos Burn Pool. The pool contract is a bank where you can deposit KOIN (for free) and get the bank's token back. You can use the bank token just like real money because that's what it is. At any point, you can redeem your bank tokens for the KOIN held by the contract (which includes profit generated through Proof of Burn). The value of bank tokens is pegged to the value of the KOIN held in the treasury.
Real world banks don't use their own money to track your balance because they'd have to worry about counterfeiting and incur real world costs. On blockchain, I can offer you more freedom with your money at no additional cost.
P.S. What would you do if you could print money for free?