You should ask instead, how it is against the Bible?

The mysteries of human enhancement was recorded in the Bible, during the events that lead to the Great Flood. Quoting directly from the NIV,

[1] When human beings began to increase in number on the earth and daughters were born to them, [2] the sons of God saw that the daughters of humans were beautiful, and they married any of them they chose. [3] Then the Lord said, “My Spirit will not contend with humans forever, for they are mortal; their days will be a hundred and twenty years.”

[4] The Nephilim were on the earth in those days—and also afterward—when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown.

[5] The Lord saw how great the wickedness of the human race had become on the earth, and that every inclination of the thoughts of the human heart was only evil all the time. [6] The Lord regretted that he had made human beings on the earth, and his heart was deeply troubled. [7] So the Lord said, “I will wipe from the face of the earth the human race I have created—and with them the animals, the birds and the creatures that move along the ground—for I regret that I have made them.” [8] But Noah found favor in the eyes of the Lord.

The Nephilim were created as a hybrid of a human and an actual angel. And as a hybrid, they have enhanced bodies that makes them inhuman. Apocryphal sources (i.e. the scriptures rejected from the canon of the Holy Bible) like the Book of Enoch even mentioned that such hybrids are significantly larger than humans, that “pure” humans are complaining to God as they commit cannibalism to satisfy their hunger.

This concept is quite similar to the inner desire of humanity who wants to be more than just a human. And here the Bible said it clearly, humanity have done that before, that finally angered God to send The Great Flood.