For one, it might be harder to attract investments from Europe or the US?
People generally invest and hire people that looks similar to them. It shouldn't be like this, but that's a very common thing to see.
-- From Wikipedia: "Race is another defining factor of Dominican–Haitian relations. The ethnic composition of the Dominican population is 73% mixed race, 16% white, and 11% black; while 95% of the Haitian population is black."
Please be very, very specific