nor that it would be good to have a general policy of smart and ethical people having less children than people not belonging to that class.

It depends on the counterfactual. If it consists of donating all the resources a kid would cost to the best cause, then that likely trumps everything. Especially also if you take the haste consideration into account; it takes forever to raise a child and good altruists are likely cheaper to create by other means. And the part about altruists losing ground in Darwinian terms can be counteracted by sperm donations (or egg donations if there is demand for that).

Having said that, it is important to emphasize that personal factors and preferences need to taken into account in the expected value calculation, since it would be bad/irrational if someone ends up unhappy and burned out after trying too hard to be a perfect utility-maximizer.