I've lost the thread of the argument now. Plus, I am tired and inebriated...
(A) Contra Chris Li, I believe in the existence of "Japanese" things. I also believe that "non-Japanese" things exist and are practiced in Japan by the Japanese people. Japanese people can tell the difference, and, so, so can westerners.
(B) I believe the dogi, while not a traditional garment, is fundamentally more Japanese than sweatpants, etc. I also believe because of its structural relationship with traditional Japanese clothes, it may/probably imparts a kinaesthetic understanding of body mechanics that is different from elastic, pull-overs, nylon, and short-sleeves, etc.
(C) I believe that people who demand an "explanation" of why dogi are necessary for aikido training are making bad arguments, be they straw-man, red herring, or some other type. The reason is that aikido is not defined by these people. Aikido can only be defined in two ways: (1) as an activity that is fundamentally universal, i.e. subject to analysis of fighting efficiency, spiritual truth, etc.; (2) as an activity that is not fundamentally universal, i.e. has a cultural context to be understandable. UFC is an example of 1--quality is judged on objective basis such as win-loss records. Tea ceremony is an example of 2--quality is judged on subjective basis that requires some cultural immersion to be accessible. I do not believe most people are willing to define aikido as a universal activity. If they did, then aikido's lack of training against kicking, for example, would lead aikidoka to say, "we should change aikido to include X% defenses against kicking," and if it could be shown that acting like an aggressive bullying a--hole was a better way to stop fights from happening, then aikidoka should say, "we should change to be aggressive bullying a--holes." And if aikido were shown to be fundamentally at odds with other objective things like a scientific understanding of the basis of mind or a utilitarian understanding of the social good, then people would give it up entirely. These types of things do not happen. Exhibit A in this line of argument is the posters who say "last weekend, we trained outside with boken but no dogi, were we doing aikido?" Why the hell were you training with boken? Boken are a culturally contextualized tool, so you should figure out what boken training aims to teach you, isolate that, get rid of the boken, and move on. But nobody wants to do that. Why? Because, in the final analysis, aikido is what people want it to be, and people want it to be culturally contextualized. It makes it more non-mundane, and this is a big reason that people choose aikido. So, I agree entirely with the poster who says that it stops being aikido when your standard of practice is without dogi or etiquette, not when you train in streetclothes a few times a year.