>Parents/families need to make the decision to give up on the positive returns of gifted education in favor of potential learning outcomes for other students or even more remote, long term outcomes of (maybe) less crime or increased tax base 20 years after graduation. I am not sure if this is a viable demand to place on parents/families given how competitive society at large is.

It's a hard, if not impossible, sell to ask any parent to sacrifice their child on that altar no matter how competitive they are.