There are many examples of people who do kind and generous things who are not Christians. Michael Jackson has donated millions to starving children in Africa. Bill Gates funds and facilitates many educational programs on his dime. Sigourney Weaver, Steven Spielberg and Eddie Murphy have all participated and given to charity, as have thousands of others.
With so many non-Christians doing great deeds, it is obvious that one does not need to know Christ to do good things. When presenting the Gospel, telling somebody they will become a better person is not necessarily telling the truth. This is proven by those who know Christ but still do bad and even horrible things.
The proof of mankind's goodness or badness is not proven with examples of good people doing bad things or bad people doing good things. It is proven by law. Every society in every country on every continent is governed by law. Property rights, civil rights and individual rights are protected through the implementation and enforcement of these laws.
The world is in sad state when people have to tell friends and neighbors not to steal from them. The depravity goes even deeper because telling somebody not to steal is not enough. There is severe punishment for those who violate the law. And still, jails and prisons are full. Laws exist because mankind is a gang of the untrustworthy.
Mankind is in desperate need of a savior. If people understand on an earthly level the logic in crime and punishment, it is hard to understand why so many are reluctant to associate themselves with spiritual principals of law. According to Jesus, there are two laws; Love the Lord your God and love your neighbor as yourself. According to Scripture there is only one punishment.
The humanistic society hates the Gospel because it seems like Christians judge others. In some cases this is true but Scripture tells us that the law is like a mirror; it shows us who people really are. It is not God who condemns but rather the consciousness of man that convicts. This is a hard pill to swallow but believers knowing who they are where they stand provides freedom. God sees everyone for what we truly are -- desperate. And he loves people despite their shortcomings. He has provided freedom from sin, hope and salvation to all.