Everyone has a place on a team, an excess of one can be toxic in a certain sense. What interests me is more the pessimist. Pessimism is certainly the minority but it has been found that the pessimist view point is more in line with reality.

Here's an interesting excerpt about the topic from a book called "Learned optimism":

Overall, then, there is clear evidence that nondepressed people distort
reality in a self-serving direction and depressed people tend to see reality
accurately. How does this evidence, which is about depression, tie into
optimism and pessimism? Statistically, most depressed people score in the
pessimistic range of explanatory style, and most nondepressed people score
optimistically. This means that, on average, optimistic people will distort
reality and pessimists, as Ambrose Bierce defined them, will “see the world
aright.” The pessimist seems to be at the mercy of reality, whereas the
optimist has a massive defense against reality that maintains good cheer
in the face of a relentlessly indifferent universe. It is important to remember, however that this relationship is statistical, and that pessimists do not
have a lock on reality. Some realists, the minority, are optimists, and some
distorters, also the minority, are pessimists.

Is depressive accuracy just a laboratory curiosity? I don’t think so. Rather
it leads us to the very heart of what pessimism is really about. It is our
first solid clue about why we have depression at all, the closest we’ve come
to an answer to the question asked earlier: why evolution has allowed
pessimism and depression to survive and prosper. If pessimism is at the
base of depression and suicide, if it results in lower achievement, and as
we will see, in poor immune function and in ill health, why didn’t it die
out epochs ago? What counterweighting function does pessimism serve for
the human species?

The benefits of pessimism may have arisen during our recent evolutionary
history. We are animals of the Pleistocene, the epoch of the ice ages. Our
emotional makeup has most recently been shaped by one hundred thousand
years of climactic catastrophe: waves of cold and heat; drought and flood;
plenty and sudden famine. Those of our ancestors who survived the Pleistocene may have done so because they had the capacity to worry incessantly
about the future, to see sunny days as mere prelude to a harsh winter, to
brood. We have inherited these ancestors’ brains and therefore their capacity to see the cloud rather than the silver lining.

Sometimes and in some niches in modern life, this deep-seated pessimism
works. Think about a successful large business. It has a diverse set of
personalities serving different roles. First, there are the optimists. The
researchers and developers, the planners, the marketers—all these need
to be visionaries. They have to dream things that don’t yet exist, to explore
boundaries beyond the company’s present reach. If they don’t, the competition will. But imagine a company that consisted only of optimists, all
of them fixed upon the exciting possibilities ahead. It would be a disaster.

In the context of the above quote, extreme optimism has a place as long as it's tempered by the pessimist. Same with the extreme pessimist it has its place, as long as its uplifted by the optimist, though what I'm seeing in reality is that part of what it takes to be an optimist is to avoid looking at reality and avoid listening or even being in the vicinity of the pessimist.