What rules are you referring to? No one is breaking any rule or law or anything really. This thread is a bad assumption about things 99.9% of the users here know zilch about.
Not talking about legality here, just the rules of game called ethereum mining.
The funny thing is the "rules" of ethereum mining are more like "laws" than legal law.
The term you are all looking for is PROTOCOL. Ethereum has a specific protocol for mining with its algorithm. Having a GPU farm, an FPGA or even an ASIC is not cheating or breaking any rule, law or protocol.
If someone does make an ETH ASIC, they won't run very long and ZEC based coins are going to start to get a lot of hashrate.