Western Civilization is absolutely not based on Christianity. Yes, art has been influenced by Christianity, but our ethics, laws, politics, and overall culture is based on Ancient Athens.
Things like Democracy, freedom of speech, freedom of religion, equality before the law, rejection of slavery, these things are all Greek ideas that go against the Bible and were not present in Europe when the Catholic Church ruled the continent. It wasn't until the Enlightenment, when we started moving away from Christianity, that these ideas became popular.
We can say that in theory Christianity is about equality because a whore and a king are equal in Heaven, but on Earth, they are not to be considered equal before the law, and only one has a career that gets them into Heaven.
I'll agree that Christian imagery is a feature of Western Civilization. And sure, Christianity has influenced our laws here and there. But outside of art and imagery, Christian influence is minimal. The ideas that became law and social norms are Greek and Anti-Christian.
The difference is that science isn't a philosophy. Nobody does something in the name of science. They do something in the name of a philosophy they think is scientific.
If there is one ethical idea that we can say is pure science, it would probably be that faith is bad unless it involves logic and evidence. And that has been a positive for the world.