Sex, drugs and rock-n-roll?
Try just sex. Prior to the 60s, the overwhelming culture was to teach youth to make wise choices, to delay gratification, to use caution and make sure you were making the right choice before doing something fun that might have consequences you were not yet prepared for.
Sex, Of course, was the paramount fun.
The birth control pill changed all that. You could have fun without consequences. Abortion became popular precisely because the pill did not always work...or people forgot to take it, etc.
You could have fun without consequences turned the focus to fun and then to happiness. In the 1950s, happiness was one of several personal qualities that were valued. But many other qualities competed with happiness.
Post birth control, fun resulting in happiness became #1 and pre-empted all other. Immediate gratification became the expectation. That led to the teaching in college in the 60s that we could have both guns and butter... both economic prosperity and a war.
There is no other thing Post WWII that has changed US culture and society more than birth control.
Well, to be fair, the Pill also qualifies as a drug, not to mention LSD and thus various hallucinogenic drugs like grass were all the rage back then. But yeah, sex is the primary part of the sixties influence.