In this case Snowden was legally required to refuse and report illegal orders. He knew the leaders were well aware of their infractions and wouldn't stop, so he couldn't just report the abuse internally.

Unfortunately, dumping juicy tidbits is the only way to get the attention needed to change things. The bad guys are spending our money lying to our politicians about it. Without showing them to be liars again and again (with the release) of these tidbits, they'd simply spin their way out of it.