This is treading on thin ice, and Cecil acknowledge that. However, I remember David Sedaris’ book, Me Talk Pretty One Day, he talks about going to speech therapy in elementary school to work on his lisp. (Well, they were trying to get rid of his lisp).
In the story, David Sedaris talks about the various kids he saw:
Answer: No. I have never met a gay man who lisps. And I’ve known a LOT of gay men.
We only do it when you’re annoying us and we want you to go away.
I knew it!
Though I did once meet a gay guy who talked without a lisp when speaking with strangers and could turn it on like a light switch when he was around those he knew.
I’ll confess I haven’t known lots of gays (and none in the biblical sense) but none of the gay men I have known had a lisp or any other speech affectation.
Never heard a gay man with a lisp. Know a few with what could be described as a lilt.
I don’t think it is that gay guys talk with a lisp - I think it is that many guys that talk in a certain manner (which may or may not include the lisp) - are gay.
I’m not sure why people frame this question as “Why do gay guys talk with a lisp?” or “Do Gays Lisp?” - I think the lisp is just part of whatever is going on with this segment of the gay population.
I had a lisp as a kid. Amazingly (to me) - it was relatively easy to get rid of. A teacher noticed and referred me to a speech therapist - and I didn’t know I had it. It was obvious once it was pointed out. Didn’t take long with a few exercises to get rid of.
Anyway - I am heterosexual - despite this - I am sometimes mistaken as gay. To the best of my knowledge it isn’t from gay guys, but heterosexual men and women. I consider myself somewhat feminine/metrosexual/non-masculine - at least compared to other men.
I really don’t care that others mistake me as gay on occasion - I’d be a little more happy if gay guys would hit on me - or women would think they need to convert me, but that never happens 
Anyway - I saw myself on video recently for the first time in a long time. I was shocked by how gay I thought I appeared. I mentioned this to several friends (these are people who would have no problem telling me the truth) . About half laughed and agreed (but all of them insisted it was pretty minor - and I was just shocked cause it was me) - and the other half couldn’t see it at all.
So not sure how helpful this is - as I’m not gay, but there is no doubt I trip some peoples gaydar. I agree that if I saw myself - I would think “he seems like he might be gay”. I’ve had at least two parents of girls I’ve been seeing think I was gay - the way I used my hands (when talking) apparently made one girl’s mom think I was. I don’t have the gay lisp, but I have some of the other mannerisms that people associate with being gay. The only reason I don’t have the lisp is that I corrected it.
From listening to callers to Dan Savage - I’d say there is no doubt that at least of the subset of males that call into his show - a not insignificant number of gay males have a noticeable way of talking that “seems gay”. Apparently this is a thing in the gay community as there was at least one call to his show talking about the bias/preference of gay men in seeking out men who were “straight acting”.
If I was gay - I think I’d have a hard time eliminating the mannerisms that make me look like less masculine. I really don’t have any desire to do so, but I did have a desire to correct my lisp. I would think non “straight acting” gay men might feel the same way. So the people without the lisp - might actually have been born with one.
Fwiw I have know gay guys that have a lisp and those that don’t.
Many years ago I was invited into the kitchen of a very high end restaurant here in LA. The entire kitchen was Mexican/Central American. They only spoke with each other in Spanish. I was told by the owner (Hispanic BTW) that entire staff was gay.
I had never heard Spanish spoken with a lisp before.
Over the past 40+ years my wife and I have had dozens of gay friends, and many more colleagues (wife) and clients (me). We’ve never known any who actually had a stereotypical lisp, but many (less than half) do speak with a cadence and tone of speech that I’m sure most people would immediately recognize as “gay.”
Although I’ve never noticed it, but wife says some of her gay colleagues would obviously be taking care to pronounce their esses.
I don’t know if this has any bearing on our experience, but for whatever it’s worth, almost all of the friends and clients have been “well to do” - not wealthy but definitely “comfortable.”
I think of the cadence as “San Francisco.” I’ve known many people from the Bay Area of all orientations with that speech pattern.
I’m gay and I spoke with a lisp through most of elementary school (I also couldn’t pronounce the R sound, much like Jonathan Woss). Both of these issues were corrected by my absolutely fantastic speech therapist.
My lisp never returns no matter how gay I happen to be feeling, but I do still occasionally stumble over words with the letter R in them. (I’m looking at you, “squirrel!”) I’ve often joked that I preferred boys because they were easier to pronounce.
I’m not gay, and I had the R-lisp in elementary school which was cured by speech therapy. My son had a similar problem, and his daughter ditto, so I wonder if there’s a genetic component? Or if it’s just very common that kidth lithp?
Try Spain.
Growing up, I sounded like a gay Elmer Fudd. My Rs were Ws and my Esses were THs dipthongs. YEARS of speech therapy and I learned to control my tongue properly.
I’d have to say the lisp in America does tend to follow that syllogism. That not all gays have a lisp, but most who have a lisp are gay.
I’ve known a few gay guys who TH lisped, but I’ve probably known more straight guys who lisped and just came off as kind of effeminate because of it.
Castilian dialect, to be exact. The story goes that a princess had a speech impediment and they copied her, since She Was The Princess. 
No guarantees as to historical veracity.
If you listen to Mocedades singing “Eres Tu” you can hear the -th- in some of the words.
One complicating factor in this is the confirmation bias problem. If a person thinks that lisps are indicative of homosexuality, and then meets Bob who lisps, they’ll conclude that Bob is gay. If they then meet Joe who lisps, they’ll conclude that Joe is gay. If they then meet Frank who lisps, they’ll conclude that Frank is gay. If someone then says to them that there isn’t really a correlation, they’ll answer “Of course there is! Bob, Joe, and Frank all lisp, and they’re all gay!”. Never mind the fact that they never actually learned the orientation of any of those men.
I am told I dodged that one because a physical cause was detected and corrected neonatally. Ankyloglossia
Not saying that’s your case, or even a typical cause, but that’s what I was told.
The quote from David Sedaris is interesting, and I know that for him (at least, this seems clear from the quote) the behaviors he describes are intimately tied in with his experience of his own sexuality. But I think what he’s describing isn’t actually a link between lisping and gayness, it’s a link between lisping and femininity, which is entirely different. (It’s the old sexuality/gender distinction.)
Castilian just means Spanish, when talking about languages. And the story goes that it was a king, I believe. But it’s not true, of course.