Playing devil's advocate as as someone non-religious and therefore from the outside, why exactly did Christ advocate against homosexuality in the first place?
Because it was not in accordance with our Creator's purpose for humanity. At Matthew 19;4 Jesus called attention to what was recorded at Genesis 1:27, 28 where it shows that Jehovah God created two genders for the explicit purpose of procreation. This was the only way the first human man and woman could "become many, fill the earth and subdue it." (Genesis 1:28)
Since all sexual activity outside the confines of the marital arrangement contravenes this divine precept, it falls under the category of πορνεία, crass sexual immorality. (Mark 7:21, 23)
