People call MC racist but truth is that he isnt one, he doesnt try to change other views about relationship with aliens, he just prefers to be with human, nothing wrong with that, EVERYONE has preference when they look for their partner, some people prefer tall people, other short, some people prefer heavier people, EVERYONE prefers certain traits in their partner.
Calling MC racist is equal to calling someone who doesnt want to date same gender as they are a homophobe.
ALso I mentioned this here before but MC is correct humanity WILL go extinct as amount of pure humans decrease, and no human genes being part of alien race may not save humanity in some way because human genes can over time vanish from alien genome especially since this alien race incorporate genes from more and more species, one day all human genes may vanish from genomes, what then ? humanity will completly case to exist from the universe.
MC is doomed to fail though as long as he is only person thinking that way, he will fail no matter waht, unless he plans to have HUGE amount of human children and he makes sure all his children only have relationship with other humans and have many children with them and so on.
With all this in mind I myself wouldnt mind being in relationship with hot alien girl ;p