The Empire has a culture of seeing Zoids as weapons more than living things. This is so prominent that many Imperial pilots don't acknowledge their Zoid's individuality, because the only way they're exposed to these Zoids is usually in the prescence of the Z-O Visor, meaning that the Zoid's individuality has already been suppressed. This means pilots don't really get exposed to the true personality of their Zoid, and with the Zoid seemingly not acting out in any way, most pilots simply accept the lack of behavior as the necessary standard. While the ethics of using Z-O Visors has been debated, most Empire pilots see no issue with it, as out of control Zoids can cause a lot of harm. Most are also unaware of the potential harm that the visor can cause to a Zoid.
Zoids are massive creatures, and even without weapons, a single rampant Zoid could cost dozens of lives. The use of Z-O Visors is only sensible in the eyes of the Empire. However, no two Zoids are the same, even among individual species. A more stubborn personality can lead to more harm. While many Zoids seem to have limited issues with the visor, a Zoid who continues to fight against its control will slowly wear down its natural vitality. The core will grow weak, its beating slowing down, and if the Zoid is forced into this subjugation for an extended period of time, the core may even bottom out, killing the Zoid. This was the case with the Gatling Fox, who only survived because Byrne Blood fled the Empire with his Zoid to save its life.
The Z-O Visor is considered a complicated technology. It's often only technicians within the Empire that can properly remove the visor, as it's noted that Byrne likely wouldn't have been able to remove the Fox's. As it turns out, it was Dr. Bowman who'd removed it for him.
The Z-O Visor was first developed by Dr. Frank Land as a means to control Zoids. This started in rougher shape, but over time, the technology was perfected and at the time of the series, it's said that newly rolled out Zoids rarely fight against the Z-O visor. One of the few exceptions was the Gatling Fox, who fought so fiercely against it, that the conflict caused by the device almost killed the Fox.