"Specifically talking about MMA, steroids are banned for exactly the same reasons they are banned in golf, hockey, bowling, etc"
The original thread posed a hypothetical situation where steroids would possibly be allowed. I answered within the context of that hypothetical situation, not the current paradigm.
"Ah steriods are not illegal but you need a prescription."
correct. While steroids are illegal for most common consumers they are not entirely illegal like Marijuana, Heroin, and MDMA.
Steroids are a Schedule III drug; meaning they have a moderate potential for abuse, have accepted medical uses in the US, and lead to low to moderate physical dependence.
They aren't regulated in MMA because they are a controlled substance that is unnecessary for a healthy individual to be using.