Wrong! Sorry..
The difference is that the hagfish won't reproduce in captivity and need an environment that is not economical if at all possible for the masses to utilize.... chickens are available to anyone, anywhere (save for a few stupid laws and ordinances which prevent it). IF the situation was reversed... we may all be eating hagfishnuggets and wishing we could have a chicken egg. It is NOT in anyone's best interest to harvest a wild animal for one thing......... the black rhino for example which is now gone, for the sake of his horn.
I doubt the poster has an issue with eating eggs or chickens so much as killing a non replaceable species for the sake of it's slime. I'd be willing to bet they may not be opposed to harvesting just the slime and freeing the fish if it were possible.