Thank you for your honesty–and I want you to know that I share your concern for the way my society has turned its back on what is right and moral. As a Christian, I believe this is displeasing to God, and that someday we will be held accountable for the way we have ignored His standards.
You also are right in thinking that Christians are supposed to stand for purity and moral living. The Bible (which Christians believe God gave us to teach us about Him and His will for our lives) tells us to "purify ourselves from everything that contaminates body and spirit, perfecting holiness out of reverence for God" (2 Corinthians 7:1). This should be our goal.
The problem, however, is that not everyone in our nation is a follower of Jesus. Our nation has been strongly influenced by the Judeo-Christian tradition, but not everyone believes in Jesus, and not everyone seeks to follow Him. Most people, in fact, are building their lives on their own desires and dreams instead of on Jesus and His teachings.
While you are here, I hope you will meet some people who are sincere in their faith and are seeking to follow Christ, regardless of what others do. And I invite you also to discover the message of Jesus for yourself, by reading about Him in the pages of the New Testament.