That isn't true!
Asia (the continent) had long periods of intermarriage with Arabs, Turks and Europeans (China, Japan, Korea, etc).
There are conversely periods where that was frowned on.
But if you look at the time period, it's almost NEVER about race, and almost ALWAYS about social status/class warfare.
Regarding homosexuality or incest it's hard to judge social reaction, for example in Greece the 'homosexuals' were actually pedophiles. There weren't many same age homosexual relationships (that we're aware of). So their reaction against homosexuality could possibly be caused by the pedophilia involved, rather than rejecting same-sex sex. Similarly with Rome.
Incest and homosexuality is naturally offensive (IMO), unlike interracial marriage, which I think explains the consistent anti-homosexual views throughout history. (incest is obviously naturally offensive, no need to investigate)
Rome and Greece are truly poor examples, since the vast majority of their homosexual acts were actually 'boy love'. E.G. a socially dominant older male with a young boy. But still they became violently anti-homosexual.
In China the history is a little more varied - Confucians weren't anti-homosexual, but many Taoist and Buddhist writings are.
Oh well ... I don't care what anyone else does. Free will and choice should be all anyone is concerned with. E.G. legalize gay marriage, legalize drugs and anything like it.