The problem is you can't enforce that you're friend didn't enable WiFi Sense without looking over his shoulder. He might end up accidentally distributing YOUR passphrase when he shouldn't be.
The only way to be sure that this doesn't happen is to add an ugly _optout line at the end of your SSID. Frankly Mr. Joe Person down the street shouldn't have to know about Microsoft's new feature to be confident that his passphrase isn't being passed around without his permission.
If you are that paranoid, you might want to implement some kind of RADIUS server. I have never looked into it myself though.