AskHistorians

Rome wasn't gay in the same way as modern day. First and foremost Rome was misogynistic. They were much more tolerant of a man penetrating another man than being penetrated, and this too wasn't consistent. Julius Caesar was a bisexual vers in today's standards. His adoptive son and the first emperor, Augustus, was by contrast a social conservative.

And so it was, you had periods of tolerance and acceptance within the culture and periods without. Then Christianity came along and Pauline sexual purity became a major issue. Long gone by then were the days of Ceasar facilitating an alliance with Cleopatra by having a kid together while both were married, and with it went tolerance of sex outside of a marital framework.

Homophobia, like misogyny, is a social technology. It could in the days before modern medicine be used to increase birth rates and reduce std transmission. But also it can enable a stricter level of social control, and allow for an internal outgroup to rally against. But it comes at a cost of human suffering.

Also what homosexuality is varies wildly with culture and time period. I mentioned the Romans and their "any hole's a goal" attitude, but you've also got classical Greece with pedorastic mentorship (but this too ebbed and flowed in acceptability) where two adult men sleeping together would have been seen as one treating the other as an inferior. Alexander of Macedon however was more like Caesar. Then there have been lots of time in the middle east where same gender sexual and romantic contact was seen as totally normal and appropriate within the adolescent phase of life, but within adults it would be seen as developmentally immature. During the Islamic golden age however homosexuality between adults was seen as normal, and in fact depictions of it were sometimes made straight when translating to Europe. But then the golden age ended and as religious extremism thrived homosexuality became persecuted.

Oh also you didn't ask but Rome always hated trans people, but we still formed a religious group called the Gallae there, who were most comparable to modern day hijra in social role and acceptance.

Fair warning this is all to the best of my recollection. My main era of queer history knowledge is post war America