Do you believe the tax system is the primary determinant of who reproduces. Taxes or none, a lot of well-off and smart people only have a few children. There are a lot of reasons not to have kids in a society that is not agrarian or if you are not living in a disease-ridden cesspool.
Poor people are always more likely to reproduce independent of belief system. They have more need for a large family to eventually support them. Belief systems, though, seem to be a large variable in how many kids people have.
There are always going to be more jobs for the poor than jobs for the well-off... so I would venture to guess that if we want a population large enough to sustain the economy, we need poor people to reproduce (considering the number of births that are accidents in all classes, it would still happen). Especially if you don't want to depend on immigrants to replace the population (which it seems from other threads, you wouldn't like). I also don't believe the government should be actively involved in telling us which people can have kids.
By all the numbers and crap, my wife and I are people who "should" reproduce... but it is not in our plan as of yet. Besides our kid would probably be against eugenics too.

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