Nature says no, we crossbreed crops and livestock all the time to produce stronger offsprings. The best argument you can make is that the offspring is no longer specialized to thrive in a particular climate as well as their "pure" parents. That said, it's not exactly ideal to have such low social cohesion that everyone's freely courting another race, the offspring will have it the worst, being forced to live their whole lives unsure of their identity.
I agree with the socio-cultural aspect of race mixing, I oppose it as to not strain the child over cultural identity, especially in America with multiple overreaching cultural and sub-cultural groups
The survey of 350,000 people across four continents did not, however, confirm a belief of a link between genetic variety and high cholesterol or blood pressure
www.theguardian.com
No. This is why America continues to be the smartest nation on Earth, we need more racemixing
Some. Not in a way that makes people of two races utterly inferior or disabled, obviously, but it can have some negative health consequences for them. I'm sure we've heard before of the bone marrow transplant conundrums that can happen.