I would say that knowing some code has allowed me to know when developers are bullshitting me. Most developers I've worked with have been great people, I'm happy to say. But occasionally I come across someone who goes "Uh-uh, can't be done, theoretically impossible, defies the laws of physics" when they mean "I can't be arsed to change the convoluted mess that is our production spaghetti code". Usually at larger institutions. Knowing some programming allows me to call their bluff.
Also, it's far more common that organisational culture, law, or the marketing department is a bigger constraint than the code stack. As a designer, I should consider my "medium" to be far broader than knowing some CSS, or I'm not doing my job.
Being a good designer is inherently being a generalist, and in being a generalist, the designer should understand some basic things about programming in order to have common ground. But that is certainly not the same as saying "designers should code". If designers should be programmers, then they should also be accountants, customer service, marketing, operations, lawyers, c-suite, and every other profession they interact with to solve a problem.