These roles were special positions, a duty for only the elite priesthood, who would know the commands and requirements for utmost purity, to enter into the Holy temple, in the presence of a Holy God. High priests should understand the consequences presenting unpure things before God. These roles require a different breed of dedicated people to be in the priesthood and wouldn't be for the likes of us.
I have a few questions:
1) What were the substances included in the formula of the authorized incense? (herbs, oils, extracts, etc.)
2) What is the effect of each one of the substances?
3) What formula did Nadab and Abihu use instead of the established one?
4) Why did they do that? Why did they change the formula?
5) Did they know the consequences of changing that very specific formula?