Is it OK if I present religion in darker tone in a novel?

As in presenting the real world religion in different fashion than what has been promulgated or ‘illicit’ in nature. Suppose that I write that Jesus was actually not saving human or that God is actually selfish and evil and that ancient people changed/have been made to change the story to hide the real fact about this. The genre will be fantasy-fiction.

Is it even legal to write and publish something of a controversial nature such as this? Will publisher feel scared of the prospect that my work might cause oppositions from the public and refuse to publish my work? Will you be offended if you’re a theist?