You guys are not being nice. This is really no different than bitcoin4cash or cash2bitcoin where people send envelopes stuffed with cash to complete strangers!
Or MtGox or MyBitcoin or anywhere else for that matter.
I concede they don't necessarily have to be nice - they are correctly pointing out that if they use my sheet, that I could be dishonest and stiff them. And when they say they can do fine without my sheet, nine times out of ten they're right.
The other 1/10 who gets stiffed, or who will get stiffed in the future, and see their bitcoins vanish, will have absolutely no clue who took them. The most they'll be able to say is "F*CK". Same with funds disappearing from bitcoin4cash or mybitcoin or in transit via the postal service. At least if someone gets stiffed with my sheet, they know exactly who to blame.