Separation of concerns != splitting logic from presentation.
SoC comes from MV* architectural patterns. In real world front end applications, people who separate based on the file extension often end up creating JS files that breach SoC - they are both handling view rendering as well as application logic inside a JS file.
If there is something that should be conditionally rendered, using JSX is no different to a template language - only thing is the variable you're using to do that isn't actually in that file either (so, over-separation of concerns?). Both of these are logic - one handles it inline and the other handles it across multiple files.
No one is advocating that JSX should break SoC (a component should never talk to an API, or implement business logic - it should be responsible for given a set of inputs, it will render the same output time and time again).
SoC comes from MV* architectural patterns. In real world front end applications, people who separate based on the file extension often end up creating JS files that breach SoC - they are both handling view rendering as well as application logic inside a JS file.
If there is something that should be conditionally rendered, using JSX is no different to a template language - only thing is the variable you're using to do that isn't actually in that file either (so, over-separation of concerns?). Both of these are logic - one handles it inline and the other handles it across multiple files.
No one is advocating that JSX should break SoC (a component should never talk to an API, or implement business logic - it should be responsible for given a set of inputs, it will render the same output time and time again).