There are two situations when the optimism may be seen as a naive outlook.
First, when the optimism is defined as a doctrine. The doctrine of Leibniz, which say that we live in the best of all possible worlds.
Now, if you look at reality in a realistically way, you’ll see that the saying of Leibniz isn’t the truth in itself. That there are so many problems in this world that may prevent you to say that the existing world is the best of all possible worlds.
Even more, if you watch TV news or read newspapers, you’ll be more inclined to say not only that this world isn’t the best, but it seems the worst of all possible worlds.
Therefore, we can say that our viewpoint may be subjective, contextual and influenced by many factors. When the optimism is defined as the doctrine that the existing world is the best of all possible worlds, we may say that the optimism is a naive and shallow outlook that don’t reflect the reality as it is.
Second, when the optimism is seen as a cheap form of positive thinking. This means that you have to repeat parrot-like positive sentences (“Yes, all is good!”), when the things go bad. It may be a kind of denying reality.
When the optimism is seen so, it can be very easy labeled as a naive and shallow outlook.
We don’t live in the best of all possible worlds, but we will try to make our world better, only if we think optimistically. A pessimistic thinking is fatalistic and gives up improving process. Optimists simply refuse to give up when are confronted with an adverse reality.
Optimists are motivated to try improving something because they assume “I can do something to change this”.
Therefore, the optimism isn’t about accuracy in evaluating the reality, but it’s all about usefulness and efficiency in changing the reality. Even so, we don’t have to deny the reality (saying that “all is good”, when the things go bad), but we have to believe that a negative reality may be improved and changed for better, if we truly want it.
In conclusion, I can say that the optimism is a productive and deep outlook on life.