The wristbands are not going to be made out of tissue paper, LOL.
Disney uses very secure wrist-bands, it's quite an effort to remove them without using scissors unless you spend several minutes trying to stretch it over your hand to remove it in tact. They are not going to fall out on a ride.
Now, a KTTW card - which you slip in and out of your pocket all day, or wallet, or lanyard, or wherever you chose to store it - is a HECK of a lot easier to lose or forget than a wrist band you have to actively work to remove.
If anything, I'd say a wrist band is far more secure as you are not removing it from places on your person all day, and you will instantly know if it's missing or not because a) it's on your visible self all day, b) you have to actively work to remove it, and c) if someone wants to steal it from you they would have to sneak up, cut it off without you, your family, or another guest not noticing, or stand there for several minutes trying to work it off your wrist. As opposed to, Dad slips the card back into his pocket - and while watching Suzy and Johnny enjoy their new balloon he either misses the pocket and doesn't notice it fall to the ground, or forgets his card at the register, has a hole in his pocket, etc.
That said, I wouldn't wear them and I think the whole RFID thing is stupid, but not for the "OMG you might lose it!" reasons, as I do think they are far more secure. I do not use them as a charge card - why put a middle man between me and my credit card company. If there are any unauthorized charges directly on a credit card, you are only responsible for up to $50 by federal law, and most card companies waive that as a courtesy anyway. By putting a 3rd party (Disney) in the middle, it's a lot harder to fight fraudulent charges as they would have to get involved as well, as the ones charging you all at once for smaller transactions you have accrued.