Everyone has made excellent points here about the brain-drain. I would add a practical consideration. Even the “loss” of 1000 people out of several hundred million could have an outsized effect depending on what skills these 1000 people have. If all or most of your top scientists left then what/who remains will be at a serious disadvantage. Imagine losing almost all of your top experts in space travel, propulsion, agriculture, medicine, mining, physics, etc.  I don’t think it would take very many such losses to have an immediate and long-term effect on your planet’s ability to compete and survive.