Im at work so cant take a picture but i got these on google and these are exactly what mine look likeCan you post a picture of the snails you have? Your description does not describe a Nassarius vibex Snail.
This is a Nassarius vibex. These are the type of Nassarius snails that do not eat healthy flesh. Notice the squat shape, heavy shell sculpting, and small slit connecting the foot to the siphon.
This is a similar Whelk that will hunt down and kill its food.
The snails in the pictures you found do appear to be of the Nassarius Genus but they are not Nassarius vibex which is the only species you should consider non-predatory.