Why does there have to be any justification?
Asking for justification misses the whole point of their rejection/disapproval to it.
I have mentioned this example before, but it's not those who reject homosexuality that are phobic, it's those who are homosexual that are phobic.
There is no cure for AIDS yet as we all know, so now is it justified to call those who don't have AIDS and who view it as a disease 'Aidophobic' or do we call those who have AIDS sick and sufferers of a disease?
Note, I am purely arguing from a non-religious standpoint.
And if there were a disease to which women were slightly more subject than men, similarly able to be ameliorated by education and safe behavior, would that justify institutionalized misogyny?
Not all gay people have AIDS. At least, in free societies with vigorous anti-bigotry laws, such as in Europe and the US, very few of those who do have AIDS are dangers to themselves or others: they know their status, they take precautions, they just wish to live their lives in peace.
The places, actually, where the spread of AIDS is least checked are all countries where homophobia and other bigotry are virtually unrestrained, or are even institutionalized in society and government. As you can see on
this list of countries grouped by highest incidence of AIDS, no European countries enter the list until number 62 (Portugal)-- the US comes in at number 63 out of 168. The top 62 countries in the world for AIDS incidence are all either African or Carribbean, places where homophobia is virulent, and anti-AIDS bigotry is uncontrolled.
Therefore, raising the spectre of AIDS to justify homophobia is utterly specious.
Hatred always demands justification for its presence. Secular societies are founded upon the premise that all people are inherently equal, and that for that reason, governments must give sound, reasonable, and verifiable justification for any infringement upon any individual's sovereign rights. It has been well established that the mere possibility of being subject to an illness is not sufficient grounds for legitimized discrimination.