Well... it is no longer the commonly accepted practice... that's pretty much a fact.
So, at the very least the statement that is it "outdated" is a fact, rather than an opinion.
Additionally, by your own admission, it is cruel since the fish will likely die. So... in a hobby where the idea is to keep fish alive, it would, at least on the surface, appear "stupid" to put fish in a situation where they will likely die...