Yes, you are right. There is nothing wrong with climate change, it has happened before, it will happen again. The problem is the timescale of the change. In the past changes occurred over centuries, we are causing the change in decades. That timescale risks catastrophe.

If you genuinely want to understand then I recommend reading Storms of My Grandchildren by James Hansen, or at least googling a few book reviews to get a sense.

For starters, moving the majority of the world's population uphill to escape the rising oceans is going to be kind of expensive.

This climate change will lead to a much shittier world for humans to live on. What's wrong with trying to avoid that?