You're asking parents to sacrifice the mental health (via bullying and social issues) (and thus physical issues likely stemming from mental health problems), intellectual development, future earning power, etc. of their gifted children to benefit others. Personally, I am not comfortable with the idea of sacrificing my children to a utopian project. These children also often develop social issues, as different IQ buckets have very different social norms (imagine how a 100iq normal person forced to socialize only with <65iq disabled folks would be affected).