Disney is probably trying to force you to wear an RFID wristband, rather than carry an RFID key card, because it is much more likely to clearly transmit over a longer range than a card. A wristband is out in the open, in clear view of the receivers all the time. The radio waves from a card is more likely to be blocked or attenuated by the body, a wallet, a purse, keys, or something else that weakens the signal. Of course, blocking a card doesn't matter if you take it out to press it against a known card reader (at your hotel door, or at a cash register, or in a fastpass kiosk). But Disney clearly wants to spy on you all the time, not just when you are purposely using your card. A wristband is going to be a better tool for the marketing spy.
Having a wristband transmit my childrens names to Cinderella frankly seems creepy and counterintuitve to good stranger safety practices you may teach your children. Generally, I think it is a good idea to teach your children to be wary of a strange adult who knows their name without asking.
It really seems to me that Disney could have implemented most of the FP+ features that might benefit customers (although the jury is still out on whether the features really are benefits over the old FP) simply by programming the old FP kiosks to print out FP+ tickets that had been reserved online. Disney is spending around a *billion* dollars on this system. Not all on wristbands for sure, but I think they could have had an effective and less intrusive upgrade for far less money. *None* of this billion dollars adds new attractions or refurbishes the many areas of WDW that are allowed to remain shabby for far too long.