I agree it’s not a real “lisp” that is the stereotype, but rather the esssses.
While a good answer wasn’t found by Cecil, I have read an interesting theory that I think is very plausible.
It posits that feminine behavior (like hissing esses and certain gestures) are learned in early child development. When a child is born there is an initial attachment to the mother that is not there with the father. In healthy development, the male child at a certain age (I can’t remember when it is) will detach from the mother and realize that they are like their fathers in a way that they aren’t like their mothers. They start to then model after their fathers in ways they don’t with their mother.
If the father is absent or emotionally distant then the child may not detach from their mothers at this time and will start modeling after their feminine traits. I’m sure no studies have been done on this, but my experience with homosexual friends lines up pretty well with this.
Not every gay man had distant fathers, and not every child with distant/absent fathers turn out gay. But, not all homosexual men are feminine and not all feminine men are gay.
However, it’s not hard to see why homosexual boys would have a higher than average chance of growing up with a distant father. Either the father didn’t approve of the child or just didn’t relate to him. Now, many children grow up without fathers but don’t become effiminate. There seems to require a higher level of sensitivity to be effected by it in this way. Homosexual men tend to have higher sensitivity than the average male (which can be a very good thing, leading to artistic ability, empathy, intuition, etc).
It also makes sense that many gay men become more feminine when around other gay men. Women do this too. While women’s testosterone levels actually raise in the presence of men, they tend to act more feminine when they are sexually interested. I’m sure there’s been studies on this, but I’m going mainly on my own observations. It makes sense, since straight men are attracted to feminine traits. It doesn’t make logical sense for gay men to do this, though, since gay men seem (according to Cecil) to be attracted to masculine traits and not feminine ones. But, in order to bring out masculinity in other men you must (I assume) be more feminine, and it’s easy to see how a group of gay men could subconsciously try to out-female each other. Most of them want to be the feminine one in the relationship (I’ve read somewhere recently that almost all gay sex personals are seeking the top, as everyone wants to be the bottom something I grew up believing would be the opposite).
It’s frustrating that so much tension and political pressure exists over homosexuality so that no truly objective studies can be done. There is SOOOO much we don’t know and we are sooo afraid of the possible answers!