Where is this rule written in this way?
You rather hilariously misunderstand the rules of hisec engagement.
The game mechanics (eg: the rules) of hisec aggression are thus: You are free to take offensive action against a target that is a criminal, a suspect, a legitimate war target, has accepted a duel or is in your corp with Friendly Fire set to Legal. Offensive action taken against any other target will result in the players ship being asploded by CONCORD and a loss of security status, said player will also get a Criminal timer, meaning if they undock in another ship while that timer is active, they will lose that ship too.
The ‘rule’ is simple: actions have consequences. CONCORD is righteous retribution, not safe space prevention of aggression.
Gankers operate well within the rules of the game. The ganker freely and knowingly accepts they will lose their ship and their security status will take a hit.
The only other ‘rule’ that is applicable here is: any action that AVOIDS the CONCORD response is considered an Exploit.
In any case, CCP has done a lot to make ganking less attractive over the years. The recent huge buff to mining ship EHP, restricting Alphas from setting their safety to Red (required for a hisec gank). Removing teh ability to tether in hisec for those with too low a sec status.
There once was a time when all corporations had Friendly Fire set to Legal and there was no method of toggling it like there is today. This led to some folk enlisting with hisec mining corps then flat out murderzoning their corpmates. One player (Awox) was so prolific at this, the term Awoxing was coined for shooting Blues/Greens.
If you get ganked, chances are that YOU did something, or didn’t do something, that made you stand out as an attractive target. Flying a Hulk or Covetor is a common one, don’t want to get ganked, fly a Skiff or Procurer. I’m only an occasional ganker myself, but if all I see is Skiffs and Procurers, I’ll go and look for a softer target.
Are you keeping an eye on local? Are you using your D-Scan? Does your mining fleet have eyes on the gate? Did you probe out all cosmic signatures in the system and check for wormholes before setting up your mining op? (most of my ganks happen because I find a hisec system in chain, pop my prober out and see hulks on D-Scan)
Your hauler got ganked? Did you scout the gate? Are you carrying a lot of valuable cargo in a lightly tanked T1 ship? Did you check your route and avoid well known choke point systems like Uedama? Did you use the Cloak/MWD trick? Hell, I near got ganked hauling a bit too much value in an Occator the other day. Cloak/MWD saved me as the Tornadoes were landing on the gate.
Ganking is part of the game. It’s been in the game since day one and will be in the game until the servers shut down forever. If CCP wanted to get rid of it completely, they would have.
So please, stop with the righteous “they’re breaking the rules”. Gankers are not breaking any rules. They are very clearly operating within the mechanics of the game as set down by CCP.
I strongly suggest you read the thread on the Eight Golden Rules of EVE