I think Paul is often wrestling with questions, rather than pronouncing on them, and the question about the potter and the clay might just be one of those times.
I don’t believe our God is an arbitrary God, as is the god of the Muslims, who can do one thing and then its opposite and both would be good by definition. I believe our God is consistent.
What purpose could there be, in deliberately making a bad or cracked pot, when you could make a good one?
How could a good father choose to deliberately teach a child to do bad, to not love him, to let him know he was born for rejection and disinheritance? Yes, that child may go astray of his own will or choice, but the merciful father receives him back when he repents.
And if the clay has nothing to lose, why shouldn’t it complain about the potter? How could it get worse?
*I think Paul is often wrestling with questions, rather than pronouncing on them, and the question about the potter and the clay might just be one of those times.*
Paul is doing no such thing.
I also believe that our God is consistent. But we are his creations and were created to serve him. We do not get to criticize God for creating us, for how he created us, why he created us. We do not get to judge what is a good pot and what is a bad pot.