The nature of the strange fire is widely debated amongst the commentators.
Was it the expression of egotism – young men resentful that the older generation would not give them a chance?
Was it irresponsibility – religious leaders who took to drink and lost their sense of what was appropriate?
Was it that they refused to get married?
The explanations which tell the story to their discredit are legion. But there are other explanations that redound to their praise.
It could be that the ecstasy of ministering at the altar transported them into realms of rapture and they lost touch with reality.
Theories of that kind reflect what today is called the numinous. Being on a spiritual high is surely something to admire, especially if, to paraphrase a description of their uncle Moses (Ex. 34:35), they “knew not that their faces shone”.
The Zohar says that they were equal in stature to the seventy elders of their generation.
Maimonides seems to have some sympathy for them but says that where they went wrong was in pursuing a sudden, strong mystical moment and not allowing it to build up patiently and modestly.
Another possibility is that they gave the people the wrong impression – implying that reaching God requires a flight of fancy instead of spreading the Divine teaching in a manageable, practical way here on earth.