The most compelling argument I’ve encountered for the existence of ALIENS, offered back in 1534 in Marcellus Stellatus Palingenius’ Zodiacus vitae:
“…we see/The Seas and earth with sundry sorts, of creatures full to bee/Shall then the heavens cleare be thought, as void and empty made/O rather void and empty mindes, that thus yourselves persuade.”
In Alexandre Koyré, From the Closed World to the Infinite Universe (Baltimore: John Hopkins Press, 1957).
From Star Trek: The Original Series (Season 3, Episode 7: 1969).
So yeah. You’d have to be a dumbass not to believe in Klingons.