Here are two of my favorites:
"For freedom of speech to exist, all conservatives must be jailed."
"For world peace to exist, the world must declare war on conservatism."
Paradox:
It's commonly known as the Theseus' Ship Paradox
Imagine the Theseus' ship (made of wood) was maintained over the years, plank by plank was replaced in the course until no original plank was left.
Now, another ship was built from the the old planks. Which one is the original Theseus'...