It would answer humanity's longest open philosophical question. The religious and social consequences would likely change the course of human history.

Imagine humans no longer fighting each other, but rather working together towards a goal. I can think of nothing that would catalyze such a change more than the discovery of extra terrestrial life. Even climate change isn't doing it.

There could be immediate peace on Earth between all mankind once there is extra-terrestrial life to hate or fear instead.

We are perfectly capable of hating them and ourselves at the same time.

How do you think the discovery of extraterrestrial life would do that? I think most people would say “that’s neat” and continue living their life unchanged.

Yes, I guess new ideas have never contributed to any change in social dynamics ever. That's the course of history you know: the social psychology and accepted wisdom is exactly as it is now, unchanged from Roman times because no new thinking based on discovery or philosophy ever led to a shift in the structure and beliefs of society.

Yeah... I would go that far. Average human's life wouldn't change in short period. But on a larger scale of time, it could propel us to explore the universe.