There are many reasons for this and it is a huge problem for our world and our people. However, the single biggest cause of this universal disregard for these moral truths lies in the common belief the only authority one must obey is one's own conscience. This is rooted in the "faith alone" doctrine which, naturally, has mutated over the last five centuries to an attitude that a person can do pretty much whatever he likes as long as he 'believes" that Jesus Christ is his savior. Today, "faith alone" has even trumped "scripture only", for now one can believe that almost any depraved act is licit, even when expressly condemned by scripture, as long as it is done for "love". So much for the two pillars of Protestantism, for it is down to one leg to stand on.
Here comes the hammer. Even if the entire lay world, every person, believed these sins, acts which go against longtime Catholic teaching, were licit, they would still be sins and to do them would be a one way trip to hell. Even if 99% of the Catholic priests and nuns were to teach these errors, the results would be the same, hell. Even if the Pope were to offer his opinion that divorce, re-marrying, same-sex unions, fornication, co-habitation, contraception, reception of Communion by people engaged in such behaviors was morally neutral, it would still be the wide, paved highway to hell.
For anyone who has been prejudiced against the Catholic Church, who cannot believe that She is the One, True, Catholic and Apostolic Church, that is the One Religion with authority over the entire human race, I offer this test. Watch the times. As things spin out of control, as almost anything goes, notice how the Catholic Church will not change Her time honored, truthful teachings, no matter how many voices within Her clamor. Notice how She will be the last one standing on these Truths. Watch how the "gates of hell' will not prevail over Her. But don't stand outside watching too long, for it is a dangerous world and to follow the world is to die.