"There are plenty of children in this country who are born into families that can't feed them -would you all advocate castration for these families too?"
Not necessarily castration but some form of enforced and permanent contraception once they've had two children. There is no reason why other people should pay, through their taxes, to support such fecklessness.
"Do you want the world to end up like China where you are penalized for having more than one child?"
Yes. The world is in dire need of a reduction in population.
"Or is it just the Black 3rd world humans you want to castrate?"
I don't want to castrate anybody but if you re-term it as enforced and permanent contraception (without the accompanying loss of parts) then my answer to that question would be "No". I want it to apply to all races in accordance with the above.