Sometimes, rules must change to balance the game. Players will inevitably find features that can be exploited in unintended ways. Even when that isn't the case, there's always room for improvement. This is just common sense. That doesn't seem to be OPs main concern here, though. Neither does cheating or ethics seem to be at the core. What seems to draw his ire is the fact that cooperation brings advantages, and he's using what seems a lot like political and ideological arguments.
Those views are very unfortunate for him, since virtually all human activity derives its success from cooperation. The moment you make a trade, even a barter, you're profiting from cooperation. The moment you use money, you're profiting from a cooperation where people have sacrificed personal gain for communal gain; they've accepted social and legal rules and restrictions. Walk on a public sidewalk, or drive on a road, or enjoy protection from the law, or run a business, and you're profiting from cooperation. Fail to return this with your own contribution, and, besides being a leech, you're also doomed to failure, as people, and, eventually, society as a whole, will stop cooperating with you.
Unlike society at large, guilds have no way of enforcing their rules, other than denying membership. That means that the freedom in a guild is considerably greater than in any country, be that the USA or China, or some Libertarian utopia. If you're denied membership, you can easily join another guild, make your own guild, or even play individually. Life as a hermit is easier in FoE than in any country; you can build your own little city, quite comfortably, all on your own, dealing with other players as if they were mere game features. However, it's a social game, and the more exciting features depend on social interraction.
If people can organize, many will. If they can cooperate, many will. If a group can profit from individual sacrifices, some will always be willing to make those sacrifices. Rather than prioritizing the meager reward of personal points, they prioritize building something that can be shared with others. Those who do this, will draw together, and, inevitably, do better than those whose selfish motivations undermine efficient cooperation. It's a winning strategy, and has put the otherwise feeble **** Sapiens on the top of the food chain, and is such a powerful instinct that it can't be excluded from any social game, and such a powerful tool that it will give an advantage whenever it's employed.
If you want to defeat someone who cooperates, you have to cooperate more and better than them. It's the only way. Fail at doing this, and you will always loose. This isn't a game rule, nor an ethics question, nor a matter of exploitation, cheating, or unfairness. It's just a fact of life. If you don't like cooperation in your guild, quit the guild. If you don't like it in competing guilds, quit competing. If you don't like it in the game, quit the game. There's nothing else to do, and never will be.
It is, by the way, very entertaining that such a freedom-loving individualist wants to impose such harsh restrictions on those who don't share his philosophy and priorities.
Edit: Added "than in any country",
and split a paragraph.