If you've never seen a slippery slope in action, ask someone else if they have. It always starts with something everyone can agree on. It's the inevitable slippage over time as the population replaces itself with people who arrn't intrinsically cognizant of the "before" state and the implicit normalization of deviance that represents. We may only live for about 100 years, but I challenge you to look at the size of the United States Code and what has been specifically carved out as illegal or aberrancies normalized just in 200 years.
It all adds up.