An argument against Molinism

[Michael Wilson]

For it happens that God does not give some the assistance, whereby they may avoid sin, which assistance were He to give, they would not sin. But He does all this according to the order of His wisdom and justice, since He Himself is Wisdom and Justice: so that if someone sin it is not imputable to Him as though He were the cause of that sin; even as a pilot is not said to cause the wrecking of the ship, through not steering the ship, unless he cease to steer while able and bound to steer. It is therefore evident that God is nowise a cause of sin.

I would disagree with St. Thomas on the bolded part. God gives to men at all times the graces necessary not to sin; if they sin, it is not because God didn't give them (us) the grace, it is because they (we) rejected God's grace.
Also, by saying that if God had given us the grace not to sin, we would not have sinned; implies that we cannot reject God's grace; which Trent clearly teaches that we can.
As to God giving men grace not to sin at all times, here is Pope Pius XII in 'Haurietis Aquas'(On the Sacred Heart).

And actually, our divine Redeemer was nailed to the cross more by love than by the violence of the executioners: and His voluntary holocaust is the supreme gift that He imparted to each individual man, according to the terse statement of the Apostle: 'He loved me and gave Himself up for me'...There is no doubt that the heavenly Father, 'who spared not even his own Son, but has delivered him for us all' being asked by so great and advocate [Christ] will at all times send down upon all men a rich abundance of divine graces."

St. Thomas was at times too influenced by St. Augustine in the matter of predestination and free will. The "Doctor of Grace" in his controversies with the Pelagians, became more pessimistic on this matter, even coming up with the infamous "massa damnata" theory, which posited that God does  not want to save all men, but out of the mass of damned humanity He chooses some out of His mercy to bestow His grace and salvation, while leaving the rest in their misery;  in order to manifest His goodness for the first and His justice for the latter.
We have to believe on the contrary that God wills the salvation of all men, and Christ died for all men; that God gives all the graces that are necessary to reach eternal salvation, and if they (men) fail, it is because they have rejected said graces, not because God has not given them to them.