I have changed your question a little bit to reflect what I think you are asking.  If I have misunderstood, please ask again.

Chelmsford was not the driving force behind the Zulu War.  He was not the one who chose to start the war.  Instead, he was the one who was chosen by his superiors to command the forces that would fight the war.  So I do not think that he would have much to say in a debate about the goals of the war.  Therefore, I have changed the question to be about his actions in the war.

Lord Chelmsford was sent to fight the Zulu War because the British felt that the presence of an independent Zulu nation would endanger their control over areas where diamonds had been found.  Because of this Sir Henry Bartle Frere instigated a war with the Zulu.

Chelmsford is important in this war because he first managed to lead the British Army to its worst defeat by a technologically inferior enemy at Isandhlwana.  He then ignored orders relieving him of command and attacked the Zulus, defeating them and winning the war.  This is what I think your debate might be about.

If I were arguing as Chelmsford, I would argue that I was doing what was best for the country without regard for my own career.  I would point out that, by disobeying orders, I was clearly putting my career on the line.  I would say that I believed that it was important to stay in command so that the Army could attack the Zulus before they were able to regroup and restrengthen themselves.  (Time had passed between the defeat at Isandhlwana and the order relieving Chelmsford.  During that time, he had won some victories and the Zulus were in some disarray.)  I would say, then, that I was willing to throw away my whole career in order to do what I thought was best for my country.