Just off the top of my head, I can think of some reasons:
1) Birth control
2) Abortion
3) Women’s lib
4) Credit cards (people can live above their means)
5) Drugs
6) Divorce (destruction of the family unit)
7) Euthanasia
8) Political corruption
I think that the real problems are #1,2,3 and 6, which I believe are all rooted in #1.
Think about it, for centuries there was no change. We went through wars before, Christianity has ebbed and flowed, and people lived through lean and decadent times, yet there was no fundamental change to society like in the 60s. What could make such a radical change? Unchaining sex from marriage is the only thing I can think of. So how do you unchain the two? Wealth won't do it, and neither will more or less religion, even condoms won't do it. But a pill that makes women not worry about the possibility of pregnancy strikes at the heart of the issue. When you could depend on women as "civilizing" because they kept sex to a minimum since they would be the ones stuck with children all of society benefited. When that broke down, so did everything else.
9) Higher taxes which forced Mom out of the house and into the workforce, which in turn enabled higher prices for the necessities of life, which .... continue the cycle ....
Women’s “liberation” (should read enslavement) caused 1,2, & 6 to grow. 2 invited 7 as its intellectual cousin. 4 & 5 are the same disease - lack of self-discipline/control. 8 is the natural result of growing government control over human life.
The Slippery Slope is real.
Liberalism is, by nature, Slippery Slop.