Just taking a wild guess, I think Jesus was a revolutionary and inspiring leader and thinker who pissed off some people and they killed him, end of story. Why we need to turn it into a whole sacrificial thing is beyond me. Was it to try to instill humility in people? "Look at what that man did for you, you assholes. What do you have to say for yourselves? Go to your rooms!" I guess we truly are God's children. His 7 year olds.
One of the (many) reasons I think our society has become more secular is that with the rise of individualism came the rise of the idea of self empowerment. Self empowerment teaches you that no one can take charge of your life like you can. You need to decide for yourself who you're going to be. You need to learn to accept, love and ultimately, save yourself; no one else will do that for you. As the wonderful Whitney Houston once sang "learning to love yourself is the greatest love of all." Truth sister. That whole thing is about finding your inner strength, non attributed to other beings but yourself and your will power (if you believe in free will, a whole Pandora's box I just opened right there).
Finally, if Jesus died for our sins thousands of years ago, he's since then been probably dying every single day in heaven because Lord knows, there ain't no shortage of sins up in this place.
(I think I may have attempted to tackle some pretty controversial and complex ideas here in roughly two paragraphs).