1: There's always a reluctance for change. It's part of human nature. We, being animals with only a limited control over our surroundings, have no choice but to live in a society by adapting to aspects of that society which we are unable to change. When change, therefore, comes from sources outside ourselves, beyond our control, it is a threat to us as it forces individuals to change their very way of life to adapt to new technologies, cultures, customs, or laws.
2: Thus, when a society embarks on change, it has to be extremely careful in these efforts. A good example is Iran:
The Shah attempted massive amounts of modernization in the 1950's through the 70's, attempting to create a massive industrial base, and one of the largest economies in the world. He promoted westernization, restored womens' rights, and established good relations with the West. Obviously, there were some initial rifts in this movement, as many of these modernizations were direct affronts to Islamic culture. Now later, the issues in the revolution expanded to include the Shah's outright abuse of totalitarian power to silence protesters, but the initial root source here was a backlash against modernization because it conflicted with old Islamic culture.
Major reforms can bring a nation to ruin or to untold greatness. The trick is attempting to figure out the way this greatness will come.
3: Now as for the brain drain issue... your very question is flawed. The cause of brain drain, remember, is the relative incentives for educated people to move to one nation or another, whether it be financial, political, research resource access, or other incentives.
You probably need to differentiate between "developing" and "undeveloped" nations, in that "developing" are actively taking steps to move toward "developed" status. Some countries here would include Brazil, India, China, and Mexico. In contrast, "undeveloped" nations would include many regions that are so embroiled with larger problems, such as basic access to food and water, disease, or political instability, that they have no ability to focus on such issues as research and development.
Among the "undeveloped" category, there is little, if any, external rewards for individuals to move to these nations. These nations tend to lack capital resources necessary for research. In addition, most of these countries couldn't even dream of paying anything near what developed nations are paying.
However, then look at the "developing" nations. China has been conducting an amazing program at recruiting foreign scientists to their ranks and training their own scientists. India, while its economic development couldn't be considered "brain drain," has increasingly gained a niche in a scientific field that makes it indispensable to the global economy. In these cases, yes, I think there are real threats, based on financial incentives.
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