I don't think anyone is interested in putting their money in a website that got hacked and had pornography and animal abuse on it, while they can't figure out why it got hacked. Instead of releasing a way to trade money over this Wild wild west, why don't they try and put some order in it first? I think they are starting to get ahead of themselves.
PayPal offers this service and has for a few years directly thru Paypal. It is nothing new. You cant just use a friends email to send money. You have to have the email and password of the paypal account that is sending the money. You have to log in first.
You can send directly to a friend simply by sending it to their email address. So I if you already have a friends info you cant be daft enough to send money from his account to a Facebook user. They will track it and do this on every purchase.
Facebook is not a very secure site. However PayPal is. Doesnt mean it cant be hacked. If you want to send money log out of Faceook and close your browser. Then Log into Paypal and send it to your friend directly.