I take it that, all things being equal, were two worlds W1 and W2 feasible for God to create, and W1 involved either more people going to heaven or fewer people going to Hell, where the number of people in W1 is neither much greater than, or much less than, the number of people in W2, God will prefer W1 to W2. Why? Because W1 and W2 are commensurably good, and W1 is ‘better’. In this case, if God by nature will choose W1 (because), then the option between W1 and W2 isn’t really a live option for God. Suppose that W1 and a discrete world W3 are just as good as each other, then W1 and W3 would be commensurably and equally good. However, according to Christian doctrine, God libertarian freely chooses to create at all, and so creation is gratuitous, not necessary, since nothing about God existing in the absence of creation makes it necessary for God to create.
However, consider God making a choice between creating any world at all, and not creating any world at all. Clearly both options may be good. God existing alone is maximally good, and sufficiently good for it to be a live option. However, there is no way to compare the good of God existing alone, and God existing along with a contingent world. These two things are not ‘equally’ good, but seem to be incommensurably good (they can’t be compared). After all, even though one can compare W1 to W2, or either to W3, how can one compare the goodness of any of these created worlds with no created order at all? However, if I’m right that this seems incommensurable, then God can libertarian-freely choose between incommensurable goods.
If a choice between incommensurable goods can be a libertarian-free choice then I have been wrong in thinking that one should have commensurable impetus for each option which presents itself as a live libertarian-free option. Suzy doing A for reason S, given an option between A and B, is explained by appeal to S, whereas if she had done B it would have been for S*, where S and S* are incommensurable.