I would change that quote a little: When people stop believing in God, they don't believe in nothing -- they believe in whatever lie Satan tells them.
There are really only two choices. Follow God, or follow Satan. There is no middle ground. Noah is Satanic propaganda. As is modern day liberalism, environmentalism, progressivism, secular humanism...
This was the plight that humanity dived into in the original sin.
At the same time now we have the quandary that nothing is perfect on this mortal coil. We do not find the perfect in the creation.
It is the use to which the creation is put that makes the difference. I think every knowledgeable Christian should know some details about this movie just because so many people have seen it. This is like the way the bible tells us a lot about idolatry without ever inviting anyone to believe in idols. Whether that means viewing the movie in person is between that Christian and God to determine.