As for seperate races... I think a large majority of the raiding community do not see any of the sizes superior to the other, which means a very tiny, but vocal majority make this out to be a huge problem. People say about 90% of the current raidingguilds are 10 man, which suggest close to 90% of those players do not see 25 man as the superior choice. Meaning they either prefer 10 man, or they do not care if it's 25 or 10 man. Notice I said "close to 90% of those players"(
close to 90% of those 90% in other words). There is obviously a few people raiding 10 man that would much rather do 25, but if we were talking about a large % of them, we wouldn't be having this many 10 mans around.
In general, people do not like being looked down on. In this case meaning they would pick the format that would benefit them but not belittle them. Being confident in their own choice, which for a large majority is 10 man, they consider themselves equal to those who have picked 25 and is obviously confident enough in this belief/themselves that they continue running the format no matter how much some 25 man raiders try to belittle them.