You're not considering timescales. True, the earth has seen all sorts of climates .. over slow-moving gradual timeframes of 100k to millions of years. And in none of those situations did human civilization exist - relying on specific climatic conditions for food, water and so on.

But now, climate is changing 1000x as fast. And we have civilization of 8 billion people, many of them living on the margins in areas that will soon became less habitable.

So you don't need Venus. Just a few degrees means hundreds of millions of refugees, food shortages, water shortages, and no doubt mass conflict as a result.

Don't confuse geologic time with human time.