First of all, I'm not having a go, I dont know much about stingrays, so I'm reading this with great interest.
A quote from one of your links:
Notes
Stingrays are aptly named, they carry a vicious sting on their tail and if cornered they will use it and they are faster than you!!! Make sure that you avoid using bare hands in a Stingrays aquarium. Rays are delicate fish which demand the best water quality. They need a lot of uncluttered floor space and soft fine substrate to bury themselves in. Normal aquarium remedies are extremely toxic to Rays so all tank mates must undergo a period of quarantine to prevent the introduction of a fatal disease. If the water is less than perfect Rays will fall victim to a bacterial disease. Don't underestimate their size or rate of growth, they need a large aquarium and nothing else will suffice.
So, your aware of the substrate issue and your aware of the venom. I'm worried your going to end up in a bad way when you put the substrate in. The fish is bound to feel threatened?
Secondly, guys, it really feels like everyone is attacking this guy for having this fish in a 180. The links support his argument, can we please explain the reasoning nehind it not being suitable for everyones benefit?