That's basically a conspiracy theory. The idea that rules against murder, theft and such aren't about the observable harm they cause and are part of some secret cabal's desire to "control people" just for jollies is worthy of Alex Jones.
"Controlling people" isn't necessary a bad thing, especially if they won't control themselves. That's why we have laws.
Right, the larger group of society doesn't accept murder and rape, and the subgroup who commits murder and rape gets outnumbered. That's a good thing.
And in reality, that scenario isn't even accurate, as there would likely be plenty of instances where the group making and enforcing the rules is the minority.
I'd argue that there are plenty of arguments in the Bible against slavery, so if some are cherry-picking parts of it while ignoring the whole then that's on them.
There's nothing within Christianity or the Bible that says similar principles can't exist elsewhere. If anything the ubiquitous of them argues in favor of them being universal. Likewise, the Bible says that sin is "common to man", so I'd argue this further substantiates the idea of universal principles of right and wrong behavior.
And while I'm not an expert on Buddhism, whether or not it specifically invokes a God, it more or less argues in favor of ultimate truths about how people should or shouldn't behave.
Right, but there are examples of social groups (e.x. drug cartels) who have little to no respect for these rules, and this type of behavior would be easier to justify by holding a purely materialist worldview. Your argument seems to hinge on the idea that "most people don't" commit extremely atrocious crimes, but, in theory, they could justify doing so much easier from a particular worldview.