https://tvtropes.org/pmwiki/pmwiki.php/Main/QuicksandSucks

TV Tropes suggests the idea whilst even existing in fiction for hundred of years before TV, is now "discredited".

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Personally I prefer more interesting madcap cultural theories. Here's one from the top of my head:

Quicksand refers to anxiety about the natural world from an increasingly urbanised and ecologically disconnected population. Or maybe Quicksand represents an increasing urban populations attitude towards nature. It represents the opposite of a safe, technology, capitalist, consumerist industrial world of the post WW2 era. Nature was literally seen as hostile. Nature can make a person stuck, capture them, and kill them. It's allied with getting lost in the woods stories, a trope which emphasizes both physical and existential disorientation in the face of nature's indifference

Quicksand on TV existed throughout the early ecological hippy inspired new age of the late 20th century but the seeds were being sown. This changed in the late 20th and early 21st centuries as we witnessed the convergence of environmental concerns (e.g. plastic bags, straws, global warming) with the logic of neoliberal capitalism, together with an increase in bureaucratic management on behalf of people. Nature is not scary but something to be protected from harm. Nature is reconfigured from a place of danger to a place of stewardship. Avatar, the movie represents the change the most.

Thus, the role of cities and technology as agents of death and destruction have changed. It is not nature that entraps or destroys, but rather the infrastructures of urbanization, capitalism, and technological progress. Ironically this valorisation of nature is happening at the same time as increasingly technological manipulation of the rural environment - mechanisation of farming, house building, terraforming, weather modification. Nature is no longer wild, is not even tame, it's another resource to be shaped and used.

Quicksand not only is discredited as being inaccurate, it's ideologically impossible for nature to be dangerous anymore.