That's not what anyone is saying. They're saying that a potter who knowingly makes a bunch of vessels with flaws in them, just so he can say, "Stupid flawed vessels!" then fling them at the wall, smashing them into thousands of pieces - isn't a very competent potter.
I think this passage partially answers the question, but it is not the complete answer, because God doesn't actually create sinners, instead he allow them to create themselves through procreation. He does this so that he can pick some vessels for mercy for his glory, and to show his wrath and power.
Romans 9
19You will say to me then, "Why does he still find fault? For(Z) who can resist his will?" 20But who are you, O man,(AA) to answer back to God?(AB) Will what is molded say to its molder, "Why have you made me like this?" 21(AC) Has the potter no right over the clay, to make out of the same lump(AD) one vessel for honorable use and another for dishonorable use? 22What if God, desiring to show his wrath and to make known his power, has endured with much patience(AE) vessels of wrath(AF) prepared for destruction, 23in order to make known(AG) the riches of his glory for vessels of mercy, which he(AH) has prepared beforehand for glory— 24even us whom he(AI) has called,(AJ) not from the Jews only but also from the Gentiles?
So the question you have to ask is. Just because you think something is unfair, does that make it wrong? If someone is richer than someone else isn't that unfair? Shouldn't we take away wealth from richer people so that everyone has equal wealth?
God did all the work, he created us, we are nothing but clay in God's hands. So if he allowed us to sin so that he could show his glory, who are you, the created, to condemn him? He has the right, as God, to do what he wills, within his nature.
Since our nature is sin, God has every justification to do what he wills with us.
That is the one issue I have with many preachers who are for predestination. They never explain why God allowed it to happen in the first place, which leaves openings to attach God for allowing it to happen in the first place.
Obviously the issue still hasn't been settled by Christians. Many of the explanations remove the power of God and rely too much on the free will of man, making God a spectator.
In any case, the doctrine of election is meant to bring strength to Christians, not to somehow convert non believers. It is enough for a Christian to know that they were selected by God, in love, rather than they made some intellectual choice and it was all by chance.