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I remember this from before 1970, maybe a tropical island? The plot had a transporter gate so anyone could go anywhere. The tropical paradise was overwhelmed by tourists...

It seems like this is happening now, with people posting beautiful spots on social media. I'm looking for the half century old story that predicted this.

The details aren't perfect, but this heavily reminds me of the novella "Flash Crowd" by Larry Niven (1973). The main focus of the story is how instant teleportation results in "flash crowds:" uncontrollable waves of thousands of people which appear at locations that are featured on the news. However, there is a section later in the story where the main character independently explores the flaws of the teleportation system. He travels to a tropical island and discovers that it has been ruined by excessive tourism.

In minutes the mall had become a milling mass of men. But he’d seen crowds form almost as fast. It might happen regularly in certain places. After a moment’s thought he wrote. Tahiti. Jerusalem. Mecca. Easter Island. Stonehenge. Olduvai Gorge.

Well--Tahiti. Say "tropical paradise," and every stranger in earshot will murmur, "Tahiti." Once Hawaii had had the same reputation, but Hawaii was too close to civilization. Hawaii had been civilized. Tahiti, isolated in the southern hemisphere, might have escaped that fate.

Jerryberry saw unease and dismay on many faces. Perhaps it was the new, clean, modern building that bothered them. This was an island paradise? Air conditioning. Fluorescent lighting.

There was beach front lined with partly built hotels in crazily original shapes. Of all the crowds he saw in Papeete, the thickest were on the beaches and in the water. Later he could not remember the color of the sand; he hadn’t seen enough of it.
Downtown he found huge blocks of buildings faced in glass, some completed, some half built. He found old slums and old mansions. But wherever the streets ran, past mansions or slums or new skyscrapers, he found tents and leantos and board shacks hastily nailed together. They filled the streets, leaving small clear areas around displacement booths and public rest rooms and far more basic portable toilets. An open-air market ran for several blocks and was closed at both ends by crowds of tents. The only way in or out was by booth.
They’re ahead of us, thought Jerryberry. When you’ve got booths, who needs streets? He was not amused. He was appalled.

Beggars. Some were natives, men and women and children, uniform in their dark-bronze color and in their dress and their speech and the way they moved. They were a thin minority. Most were men and white and foreign. They came with their hands out, mournful or smiling; they spoke rapidly in what they guessed to be his language, and were right about half the time.
He tried several other numbers. They were everywhere.
Tahiti was a white man’s daydream.