"Why would you want Bitcoins instead of cash?". For a second I didn't know what to say; then I thought about it and here is what I came up with. Feel free to contribute to this.
1) More security (especially if you are careful).
2) Bitcoins are a potential investment, cash is not. Paper currency only really goes down in value, Bitcoins have a lot of potential to be worth more as time goes on.
3) Fast, worldwide transactions at your fingertips.
4) Similar to #3, but it's a universal currency. It's legal in most countries of the world and you don't need any kind of currency conversion to send money to people in a different country than your own.
bitcoin is more secure than cash. and you only have a gadgets to do transaction with your bitcoin instead of carrying a big wallet that full of ID.
a lot of hard time transaction in cash, but somehow easily deal with bitcoin. some other point, bitcoin increasing its value day by day unlike the paper currency. and you dont have to worry if somebody hold-uping you because they will not get your money because you didnt carry any of paper currency. unless they know about bitcoin.