Why do many gay men speak with similar inflections and syntax, regardless of place of origin, ethnicity, or age?

Because it's a learned cultural affectation. My understanding is that as the gay rights movement became more visible in the late 60s in urban centers like NY and San Francisco, the very vocal/visible icons that emerged began to be very subtly emulated in their speech and mannerisms, and over time it's just become part of the community. The same thing can be seen in any social culture, like kids in the inner city, or more clearly, affluent kids in the suburbs, emulating kids in the inner city. It's all just learned behavior.

I think its a learned behavior--and one that really maifests itself differently in different parts of the world. I think often as young gay men are coming up in the world, we need a visible or audible identifier--something that makes us feel part of something, rather than cast out of something. speaking with a certain inflection is one way gay men identify themselves to eachother. this is just my take on it--totally anecdotal.

I've noticed that other groups speak in similar ways as well. Staffers and legislators talk in a monotone whether working together or testifying in public. You can hear this drab language on the radio in news reports.

Also, young girls seem to have a raspy whiny sound, late teens, early twenties. I've heard it from different girls from different places. It's what distinguishes them, however unconsciously.

Perhaps those who work, live, or love together talk the same.

It's Eunuch speak. If a man were castrated as a child, he tends to have a high voice that sounds feminine, yet is identifiably male. When people self-identify as gay, they adopt this mode of talking, because it has been used by feminine men for a long time...

i'm pretty certain it's not "eunuch speak." that sounds pretty absurd, bordering on offensive.

It's learned I believe, because I can totally tone down that "gay quality" to my voice when I need to. Haha

maybe the reason is :gay’s love is different from the girl and straight!:)