I've heard this story a number of times, but to make sure I had it right, I looked it up in a little book entitled The Power of Stupidity.
A scorpion wants to cross a river, but it can't swim. It asks a frog for help. The frog is apprehensive, but the scorpion promises, "I won't sting you. If I did, I would drown!" So the frog takes the scorpion on his back and ferries him across the river. When they reach the other bank, before he gets off the frog's back, the scorpion stings the frog.
The dying frog asks, "Why? I've ferried you across the river, and now, after doing you this favor, you repay me by stinging me! Why!??"
"Because," say the scorpion, "that is my nature."
Look at history. Look at the nature of fascism. Then, think about the frog and the scorpion.