I cannot believe these people. Reminds me of people who find it amusing to put a cat in a bird cage.
I don't know who those people are on that forum, but I would doubt they have the knowledge level of cichlid sources like Kullander, Loiselle, Newman, etc. I know some of these people, I may run this past them this week. Mind you, if you are talking shell dwellers, that is a bit different. Finding fish suitable to hard water is not all that difficult; it is the aggressiveness of the fish and the habitat that is the issue. Shellies tend to keep themselves to themselves, and are not likely (as far as I know) to go out and attempt to kill off other fish in the tank. The size of the tank also factors into this.