Eliza, they are very religion based. Homophobia is almost exclusively religion based. We get our hard wired hatred of others from scriptural justification over the ages. The success of this is in how many people who aren't religious still harbour bigotry encouraged from the pulpit to their ancestors. Even now, the established churches cannot bring themselves to see everybody as "God's children."

The European missionaries did their bit to stamp it out in Africa and elsewhere in the name of god.

And that is, according to Archbishop Desmond Tutu where the fun began.

Screening for HIV would pick a few more up on entry, as far as immigration is concerned. But only for those unaware at the time who are symptom free.   The overwhelming majority declare their status rather quickly. Sadly, the lure of free care and drugs is one of the categories in what we call economic migrancy. Communicable disease doesn't fall into this government's denial of access to care. We have to treat such conditions regardless as a public health measure from arrival.