I've enumerated some. If people want to live in a society that isn't their "native" one, then they need to learn the language, adapt the culture and customs and do things that others in the society do. As I wrote above, "When in Rome, do as the Romans do." One cannot expect to be accepted into society if one doesn't meet societal norms. Nobody is supposed to abandon their heritage, but that doesn't mean that they cannot adapt.

Actually, I'm the one who brought up the ID card issue, not Skandalouz.
What someone wears definitely has to do with their ability to perform in a workplace. Take, for instance, the banking industry. If a person dresses conservatively in a bank (in the United States, this means at least slacks, shirt and tie for gentlemen and the same or a business dress for ladies), then they portray to the customer the image of stability which is necessary for the customer's perception of safety of their money. If a person dresses in an unconventional manner in that same position, the result is that a customer is less likely to feel comfortable depositing their funds in that bank. This is true with most industries that have customer interaction. The clothing that one wears directly impacts the customer's view of that business.
From a business standpoint, therefore, it is reasonable to reject any applicant who doesn't adapt to the societal norms of dress for a given position. If the position requires casual clothing, someone dressed in semi-formal wear might be rejected because it appears that the "overdressed" person doesn't understand the position. Similarly, if the position requires semi-formal clothing, an aplicant in neat, but casual clothing may be rejected for the same reason. It may not be "fair" that this happens, but it does happen and for good business reasons. In my experience in hiring interviewees, I have seen people in many styles of dress and appearance. Depending on the job that I was hiring for, I sometimes discarded certain applicants out of hand based solely on appearance. The proper appearance gives the employer the idea that the applicant at least understands something about the job and can take it seriously.
Businesslike definitely has to do with clothing as well as attitude. A person with a perfect attitude may still not be businesslike if that person dresses in ripped jeans and a T-shirt to an interview. Similarly, ethnic traditional clothing may be inappropriate for a particular job and an applicant dressed that way is likely to be rejected for that reason.
Yes, this does indeed mean assimilation at least in one's professional life. Assimilation into society is indeed discrimination, but it isn't (necessarily) racism. Let me state that many times discrimination is perfectly acceptable. For example, I as an employer, might give a benefit to one employee that I don't to another. That is discrimination. The reason that it may be acceptable is that the particular employee may be the best employee that I have, and it may be a reward for good work. Similarly, it is acceptable to discriminate against a poor employee by refusing to extend certain benefits (e.g. permission to leave early).
You are indeed correct that what we refer to as "race" is simply a variation within the human species and those who discriminate because of it are really being foolish since there is really no difference. Nonetheless, stating this obvious fact doesn't change the world. Until people choose to ignore skin color, then we have to deal with it. The best way to deal with it (in my opinion) is to show those who discriminate that those of different skin color are in fact capable of doing the same work and living in the same society. To do so, members of the minority must remove as many "differences" as possible (in their professional/public life) so that the only difference that can be perceived is skin tone. That would leave the racists without any legitimate excuse other than racism if they discriminate. Again, I'm not sayin that the minority must abandon his faith or culture, simply that in one's public/professional life, that one should assimilate in appearance. What someone does at home doesn't matter to an employer unless the employee brings it to the workplace.
What we see instead is minorities trying to force their differences down the collective throats of the majority with the result that the majority can come up with many legitimate reasons to reject the minority because of those differences. Moreover, such an approach is often viewed as hostile by the majority and they will likely react with hostility in return which leads to a worse situation for the minority, not a better one.
The next step, after a minority group has become integrated into society may be to work from within to gain acceptance of their own cultures in the greater society. This is what has happened with many minority groups in the United States. There are still many others where this has not occurred, but in those cases, we don't find the integration.

That's true. Ideals are ideals because they suggest the best possible outcome. A realist knows that there are people who won't follow the ideal. That isn't to say that these people aren't generally decent people, but they are flawed, just as the rest of us. Making policy based on an ideal (as Chirac did in France, forced diversity acceptance) is simply unrealistic (and, predictably, it didn't work). Better to make a policy that accepts the flaws and still attempts to provide an equal footing (assimilation into the current society).
Discrimination based on dress isn't intentionally malicious. It is simply a business decision. Business is amoral. It doesn't care about social graces or right and wrong. It cares about profit and loss. If a business person feels that certain dress is incompatible with profit, they can choose to prohibit it or reject an applicant for it and that would be a legitimate decision based on business needs. I'm not saying this is a good thing, but it is reality. We all live in this reality, and whether we like it or not, denying that it exists leads to unrest and to situations like the one that France is facing.
Societal norms (including dress) is indeed ethnocentric. That isn't the same as racist. French society is what it is. Perhaps one might disagree with it, but if one wants to live in France, it is unreasonable to expect French society to change, it is more reasonable for that one to change to adapt to the society.

-- Jeff

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"Government is not the solution to our problem, government is the problem." --Ronald Reagan