Some people think that "God created the reprobate just to torture them in Hell for all eternity," is an accurate picture of one aspect of Calvinism. I've heard it used a number of times as an attempt to criticize Calvinism. What's a good answer when someone asks you if that's what you believe - or claims that it's what's implied by your belief.
1. The Short Answer - the Tulips
One short answer is that it's like saying you buy your wife flowers, just to throw them in the trash. That's where they end up, right? But isn't it absurd to suppose that their whole purpose is summed up by their destination? The real purpose of the tulips is to beautify the house for a short time. Yes, they are going to end up in the trash or compost heap, but that's not their primary purpose. It's equally as absurd to suppose that the primary purpose of the reprobate is their destination in the lake of fire. There is more to their lives than that, more to their existence than that, and God uses them in other ways than that.
2. The Longer Answer - Your Ancestors and the Tulip Revisisted
We don't know all the purposes of God, or all the reasons he has for doing the things he does. Many of your and my ancestors were reprobates, but God used them to give birth to people who gave birth to people who ... gave birth to us. Without them, we would not even exist. I don't think that's the only purpose God had for them, but it's a purpose. They played other vital roles too. You are not an island, and neither were your ancestors. You and many of them were protected, served, nurtured, and supported by people who were reprobates. So, the role of reprobates in your own life and very existence is enormous - probably beyond anything you can directly comprehend.
But let's go back to a tulip. If you look at an individual tulip cell under a microscope, it may be hard to see it's purpose. Maybe the particular one you see has a particular pigment to it, which helps to provide the beautiful color of the flower - but many of the cells don't have that pigment. There are a lot of cells in the stalk or the leaves. If you are looking at them under the microscope, you can miss the bigger picture of their role within the tulip plant as a whole. The same can be true of an individual human.
Each human is not the be-all and end-all of the universe of Creation. The individual is like a tile of a much larger mosaic. Unlike a mosaic, though, God has crafted each tile. The tile is not just found and put into place opportunistically, but is specially designed for the purposes it serves in the vast drama of history.
So, the question is wrong because it is both myopic and narcissistic.