"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 much better now than cash because it is also much safer and that is because you cant be robbed on the street so that is also much better but maybe you can promote it also more.
And that would be perfect but you never know what is going to happen with the value of Bitcoin.