The fundamental principle of Christianity is to love one another, as Christ did.
Jesus of Nazareth existed as a human.
The fundamental question becomes was Jesus divine and did he rise from the dead. Certainly it is possible to acknowledge the positive message he proclaimed even if one denies his divinity.
Christianity is not about feeling persecuted by the guilt of one’s sins.. It is about loving Jesus and following his example to love, while understanding we will always be sinners...Christ does not expect perfection from his followers ( remember Peter’s denial) We may have many atheists because the true message of Christ is missing from many of our churches.
I suggest you look again.
That is not a principle but an ethic. Ask yourself what the principles that ethic is based on.