Outside of registered trademarks, no one really has a "right" to a domain name. If the Mormon church couldn't buy LDSMatch they'd use something else. Now it's obviously financially or otherwise beneficial to them so they are willing to pay for it, but that's not really a need.
If there was a rule, squatters would just put up a WordPress blog with two posts.
If there was a rule, squatters would just put up a WordPress blog with two posts.