I think genocide sounds a little extreme, but I do understand what he means.
In thousands of years it is quite realistic to think that the Caucasian race will not exist. Just like at some point there will be no full blooded aboriginals.
Immigration is basically confined to those countries with Caucasians. Of course, we are not talking about 100 years, but it is feasible that it will happen in time. I don't think genocide is the appropriate word. Us Caucasians would take offence to an aboriginal coming out an accusing us of genocide over the last 50 years. People choose to breed with whom they want and are not forced to do it. So while I don't agree with genocide, I can see what he is getting at.
It will happen because other countries won't allow it to happen.
