There’s a reason why Scorpio is a fixed sign, and there’s also reasons why people tend to question how Scorpio is fixed at all. Scorpio however, will always be a fixed sign.
The questioning usually starts due to the planets ruling Scorpio. When people think of the fixed modality, they tend to think of keeping something stable, calm, or static, which is the technical definition of being fixed. However, Scorpio shows that you don’t always have to try to be comfortable and safe to feel stable with yourself. Scorpio actually proposes the opposite: you can gain stability and fixation by being doing the counterintuitive – being volatile and extreme. It implies that sometimes, in order to be truly maintain stability, you must go out of the comfort zone to get it. This is explained through Mars traditionally ruling over Scorpio. Mars always presents an energetic, argumentative energy that goes against the nature of staying unchangeable. That’s why Scorpio is always seen to be a polarizing sign, but that’s not the only place where Scorpio’s extreme nature comes from.
Pluto is the other reason why people can question Scorpio’s fixed modality. Pluto represents transformations, which is an impactful change. When placed next to each other, what Pluto represents also contradicts with the fixed modality. It almost seems that Scorpio is too dynamic to be a fixed sign, when really, Scorpio uses change to maintain stability. You may ask why Scorpio would want to be stable in the first place.
Scorpio wants to be stable so that it can stabilize the inner chaos it has inside itself. After all, stability is the core principle that holds Taurus and Scorpio together as sister signs. Stability and control is what gives Scorpio’s seemingly dangerous volatile nature a sense of direction. Without the idea of stability, Scorpio would truly be a sign of disorganized chaos… But Scorpio is not. Scorpio represents organized chaos. After all, you never see a Scorpio lose its composure in public, since it is good at keeping a scarily calm demeanor. Scorpio will also fix itself on something powerful, but tangible to keep themselves together. This is why Scorpio is known to keep secrets.
The fact that Scorpio is also a water sign also explains its fixed modality. Emotions is the main medium used by the water signs, and emotions are quite fleeting, dynamic, unstable, and irrational at times. Naturally, emotions are preferably (but not always!) hidden for the water signs, and for Scorpio, it keeps its emotions hidden to keep itself in line.