They are still fish, just not what someone was wanting or expecting
I guess it would depend on what the hybrid is. For people who take their breeding seriously, keeping a line pure is very important.
For example, the Victorian Basin Cichlids are endangered. Making hybrids of these fish, and then distributing them, could muddy the bloodlines to the point that no true blood of these species exist, anywhere. Not in the lake, and not in our tanks.
The next problem with hybrids is aggression levels. You may not know what traits will come out in a hybrid. You may have one that goes on a killing spree, and empty your tank.
A lot of species are really cool enough, without having to make hybrids. Keeping hybrids is a personal choice, but distributing them without knowledge is unfair to the people that would purchase true blood fish.