My take is that Capt. Carey got alot of bad press.
I would think it would be hard to tell a Prince that he could not do this or do that.
After the Prince was killed, they had to blame someone.
After all Carey was " in charge."
As is probably obvious from the OP, my sympathies lie with Carey. In fact, I think that if it was me given that assignment, I'd have been shaking in my boots. That was a mission that could only end in oblivion or very badly for the officer in command.
However, let's try the Devil's advocate position: My understanding is that neither Carey nor any of his troops fired a single shot. Is it possible that the prince got so far ahead that they could neither see nor hear him? Or did Carey simply not want to risk bringing the Zulus down on
him?
The primary charge of cowardice against Carey was laid not so much because he didn't fight but because he and the couple of other scouts (three? four?) actually paused to meet and wheeled round on their mounts to look on the scene without so much as firing a shot at the Zulus.
...I find it interesting that the scouting party didn't take a swipe at the Zulu band that ambushed them.
Granted, he was on a scouting mission, not a "let's see if we can kill the whole impi by ourselves" mission, but still... one of their own had gotten into a mess.
Also, there remains the fact that word got around in the army itself that Carey had acted badly, not just simply in the civilian press.