Why? As a member of an organisation, you represent it, willingly or not. It's no different in the "real world", as this case highlights. What do you find so repulsive about it?

In this case, the problem is that you don't choose to be a member of a school; your parents make that choice for you. Bad behavior on the part of a child should not reflect badly on the school, because, you should assume, the child does not want to be a part of that school, and is doing anything they can to reject their status as a "member." It isn't the school's fault that there are parents who live in the area, who have a child who must, by law, attend that school, and who does not want to attend.

And, because you can't measure the school by the individual, you can't measure the individual by the school, either. If a school has a reputation for kids behaving badly, that probably just means that a bunch of the kids who go there, who don't want to be there. Whether they wanted to be there when they arrived at the school is a separate issue, amenable to causal analysis.

...Now, similarly, a lot of people are forced to work at jobs they hate for a paycheck...

The simplest way I can explain this to you is that for various reasons some people enjoy conforming, others don't. And, this case highlights different things about the "real world" to different people.

If you don't want to conform, don't wear a uniform identifying you with the group you don't want to conform with.

Sorry for the confusion but was just answering your question, not talking about myself. I don't wear any uniforms. Interesting view though, considering we're talking about primary through high school students. Not sure how many children have the power to choose their own school. I'd imagine most don't have that choice and therefor are identified with groups they had no hand in choosing.

edit: just noticed the another commenter already pointed this out to you.

(I didn't ask you the original question) I was referring back to the original situation, a guy at a conference representing his employer and signifying that by wearing their brand. By 'you' I meant the generic 'you', really.