Transhumanism is simply a modern, technological derivative of the Christian contempt for the natural human body (“the flesh”) and of the Christian desire to live as a disembodied soul in a paradisiacal heavenly afterlife.
A strong, healthy man doesn’t have any problem with living in a human body. A strong, healthy man is able to rejoice in his physical well-being and excellent constitution, and it is an excellent thing for a strong, healthy man to be able to enjoy his body fully and completely.
On the other hand, a weak, diseased man must necessarily despise his body, and must therefore hate his life in a physical body. This is the thinking at the origin of the Christian tendency to be in contempt of the body (i.e. of “the flesh”), to consider the body to be nothing but a loathsome vessel, or even something like a hellish prison.
In recent times, the Christian desire to escape the physical world into a non-physical heaven has developed into a hideous fascination for existing as a machine, or even in a machine. Transhumanists would rather live in an artificially contrived existence than live a natural life in a natural body because transhumanists profoundly despise everything natural, including the natural human body.
The basic thinking of the Christian and of the transhumanist is essentially the same: that life in the natural, physical world is contemptible and despicable, and that being able to escape the confines of the natural, physical world is eminently desirable. And this thinking can only arise from the minds of weak and diseased people.