Harmful is wrong word: "less effective" is more realistic. The title of this post is clickbaity. The "goto considered harmful" was the start of this and the overall pattern has not improved with age.
Most mouse GUI actions don't require complex curves even when they appear to. You can see this when you look at GUI recording and automation scripts generated or supported by tools such as Sikuli [1]. The better approaches don't even require precise coordinates for most actions let one complex curves/lines.
What the mouse does provide is a suitably generic input device that allows exploration and discovery. A strict CLI style user interface doesn't tend to have this level of possibility without rapidly becoming overly simplistic. Readline support is a good attempt for most realistic use cases but still requires a learning curve.
Final note for people who think mice are intuitive: back in the day I had to train people on how to use the mouse button to click a onscreen button. The two events are not inherently obvious - they just appear so now because our culture has now adopted it. The bar has been raised.
The argument makes sense, however for some things a mouse is simply faster than anything else, including a keyboard - and more compatible. For example, I browse the web mainly via the keyboard thanks to Vim bindings, however often it's simply faster to just click a link than doing it by hitting 3 keys. Not to mention many websites build their UI using some JS frameworks which somehow prevent the browser from recognizing any UI elements. This is especially frequent in cookie notifications and newsletter popups that usually can't be clicked away without the mouse.
And while I prefer the keyboard for most interactions, most users would probably find the mouse more convenient because the mouse is almost always easy to use without memorising any shortcuts. Every website and program is fully accessible with the mouse, but the same can definitely not be said about the keyboard nowadays.
"Using mouse is more effective because mouse is more popular with designers, and thus controls are mouse-only." Nope, that doesn't follow at all: "someone _made_ it artificially hard to use keyboard on their site, which proves mouse is more efficient" - that just indicates laziness, not to mention ADA noncompliance.
Most mouse GUI actions don't require complex curves even when they appear to. You can see this when you look at GUI recording and automation scripts generated or supported by tools such as Sikuli [1]. The better approaches don't even require precise coordinates for most actions let one complex curves/lines.
What the mouse does provide is a suitably generic input device that allows exploration and discovery. A strict CLI style user interface doesn't tend to have this level of possibility without rapidly becoming overly simplistic. Readline support is a good attempt for most realistic use cases but still requires a learning curve.
Final note for people who think mice are intuitive: back in the day I had to train people on how to use the mouse button to click a onscreen button. The two events are not inherently obvious - they just appear so now because our culture has now adopted it. The bar has been raised.
[1] http://sikulix.com/