The core grounding objection is 'how can counterfactual statements about a persons libertarian free will be true, given they do not actually make the choices in the real world?' Molinists may respond that God's unique ability to hypothesis enables Him to know what hypothetical people would do in various circumstances. At this point grounding objectors may take two distinct approaches to furthering the grounding objection. The most forceful is that asserting grounding for counterfactuals of freedom is illogical, because it entails a contradiction. The weaker response the grounding objector may take is to say that such grounding is implausible and it contains counterintuitive elements.
Plantinga and Craig have refuted the stronger grounding objection. Thus Plantinga states "It seems to me much clearer that some counterfactuals of freedom are at least possibly true than that the truth of propositions must, in general, be grounded in this way."(link) This move may seem like a shift of the burden of proof, but keep what the grounding objector is doing is asserting that only realities and possibilities may be the basis of truth for propositions. Thus they must carry the burden of proof of their assertion. And what proof can they offer? What reality or possibility grounds the truth that only reality or possibilities can ground truth? The grounding objector cannot even claim that such a principle in an axiom, because the very principle if true, requires grounding. The grounding objection is ungrounded.
Next, God willing, we will look at the weaker objection, that the grounding asserted by Molinists is implausible.