Here's another reason why it makes sense to have hope. It's clear that as our stock of knowledge and information grows, the population of solutions grows. We've learned, for example, that many mental problems are the result of imbalances in blood chemistry. Millions of people have achieved dramatic relief through the use of a growing number of pharmacological treatments. That's just one example of how greater knowledge has reduced human suffering.
Some people tend to think that every new solution creates a new problem.
Solutions do cause change, and with change there are gains and losses. The clearest and most significant achievement of science and economic growth is our increased life expectancy. This advance, however, has caused Alzheimer's disease to be far more common than it used to be. I would argue that the population of major problems is almost static, that most of the large problems and challenges of the human condition have been with us for thousands of years. Besides logic there is also historical support for optimism.