But it should, in theory, always ask you to click a confirmation before doing anything... But yeah, NFC and S-Beam are not the safest of technologies out there. HOWEVER, remember what NFC stands for: NEAR FIELD COMM. Near Field. Near. You'd have to be close enough for someone to touch the back of your phone for them to do anything malicious.
BTW, so is walking around with Bluetooth On the entire time... in theory it should ask you to pair first, but it's also a security risk. Yet, most people don't even know an On/Off toggle exists. (OK, maybe not 'most' hehe but a lot of people just leave their BTs On and worse, visible)