Although it is important to avoid stereotypes, at least some of them could be true to some extent. For example, not all Japanese are polite but relatively speaking (i.e. compared to people of many other nationalities), Japanese are quite polite in a more frequent manner (except when the senior deals with the junior, for example), given their language, education, social norms, etc.

I have also noticed an academic tendency to argue for something in a quite distorted and exaggerated manner partly as a result of their enthusiasm to reject stereotypes. For example, I understand that the stereotype of 'homogeneous Japan' cannot be 100% true.
Conservative politicians often over-emphasise Japan's homogeneity as a political tool to impose their nationalistic values. There are a number of minorities such as Ainu (although they have already been quite assimilated as a result of a Meiji policy of 'domestic imperialism'). In addition, Korean and Polish societies can be even more homogeneous than Japanese. However, again relatively speaking, Japan is quite homogeneous when it is compared to 'multicultural' societies such as the US and Australia. It is quite exaggerating to over-emphasise 'multicultural' aspects of Japanese society and consider Japanese homogeneity as a 'myth'.
In reality, foreign population in Japan is less than 2% of the total population and about 80% of them are either Chinese or Koreans, who can be quite identical to Japanese physically. If we add nikkei Brazilians, the figure becomes around 90%. Even in most parts of Tokyo (except for a small number of places like Roppongi but including places like Shinjuku and Shibuya), it is an 'occasional', not frequent, thing for the Japanese to see the people of different races (i.e. most people look like Japanese on the streets, trains, etc.). This situation is very different from cities such as New York, Sydney, Paris and London.
Japanese national immigration policies are not oriented to multiculturalism, either. Although I understand that some academics have strong desire to debunk Japanese nationalistic statements related to racial homogeneity and Japan is now more multicultural than 20-30 years ago in its own terms, calling Japan a multicultural society without looking at the situations in other countries seems another extreme thing. If ordinary non-academic Japanese people are told that some academics argue that Japan is multicultural, I guess most Japanese people would consider it as an example of 'academic nonsense', especially if they consider the situations in the US, Australia, etc. It is important to have a comparative perspective so that we could avoid creating another 'myth'. It seems that this comparative perspective can often be acquired by living in different countries and mingling with (and also having relationships with) people of different nationalities.

Hiro Watanabe

P.S. As for the usage of the term 'ojisan', I think whether one is considered to be ojisan or not ultimately depends on how one looks, although actual age may also be relevant to some extent. For example, even those in their 40s and 50s (or even older) may not be considered as ojisan or oyaji if they look relatively young, smart, handsome, etc. In this case, they might be called 'kakkoii hito', 'shareta otoko', etc.

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Dr. Hiroaki Richard Watanabe, D.Phil. Oxford Lecturer, School of East Asian Studies, University of Sheffield

http://www.shef.ac.uk/seas/staff/japanese/watanabe.html
http://www.wreac.org/people/WREAC-People/Core-Researche
rs/Watanabe%2C-Hiroaki-Richard/details