God did make it His plan for everyone to enjoy eternal happiness; but He created creatures with freedom to love or reject Him. The admittance of a creature into the intimate life of God, is such a great privilege, that it is not forced on anyone. Also, because God is infinitely just, He would not do that which would be contrary to justice by admitting those into His friendship who would not have earned it. The reason infants are now admitted, is because of the merits of Our Divine Savior.
There is still omnibenevolence, its just that we wont see it completely until the final judgement, when all the secrets of God's goodness and the ingratitude of those who rejected Him will become manifest.
I think we've arrived at the heart of this dilemma, Michael Wilson. First, we can logically follow the scenario where God has provided many souls with eternal happiness without any use of their free will: we can follow this to the simple conclusion that it does not contradict the notion of an omnibenevolent God.
Then, we can look at the scenario where God has created a scheme were there is suffering, even eternal suffering, and see that this does, at least,
prima facie, contradict the notion of an omnibenevolent God. It remains possible, of course, that there is some unknown way that God could create this and still be omnibenevolent. But that claim is suspect, as it appeals not only to what we do not know, but also to what appears paradoxical and illogical.
Therefore, absent faith by grace, wouldn't the logical conclusion of finding a world with suffering be that it was not wrought by an omnibenevolent deity? An omnibenevolent diety would, definitionally, give to all created souls eternal happiness,
gratis.