Well...you'd have to invest heavily into globalized education..but you would being fight social stigmas and entire cultures , oh and then there is the battle of persevering cultural diversity or trying to unifying everyone for the the good of the species. What else, you could remove borders or any sense of nationalism,patriotism, religion, language, ethnic identity. That would all have to go with education but again you'd have even more problems than results in trying and unite humanity this way. Then there is physical homogeneity in our species, that could help, so genetic engineering for a homogenous looking human race... eugenics... but we saw how those attempts fared out in history and that just raises even more problems. What else...Oh! Remove the instinctual pack and tribal mentality that divides us to being with...i doubt that will happen any time soon..or at all.
So basically...so long as their are realms for any difference, social stratification, ignorance, which all feed into the "us" vs "them" mentality, i doubt we can completely stop the dehumanization of our fellow human beings, without giving up our own humanity in the process.