The earth is slowly degrading. Global warming has melted the Arctic, pollution has ruined water, and ecosystems are disappearing. If humans can find a planet like Earth elsewhere, humankind can colonize the planet and continue their existence outside of Earth.
If the planets near Earth can’t be colonized, there’s no guarantee that other planets outside of the galaxy can. There are too many unknown variables that could affect the success of colonization. If there were viruses on an Earth-like planet, sending humans there would be devastating. The easiest thing to do is improve Earth’s health instead of actively looking for an alternative.
[P1] The Earth is slowly degrading. [P2] The goal of space exploration is to look for new planets like Earth. [P3] Space travel will ensure humankind’s existence when the Earth can’t support us.
Rejecting the premises
[Rejecting P2] Although the earth is degrading, it has shown time and time again that it can regenerate its ecosystems and atmosphere. [Rejecting P3] Space travel is not guaranteed to find planets to establish human colonization.