Venus » Saul did not extend his waiting (waited for seven days) for Samuel indefinitely, but went ahead and made the sacrifice himself. This good-intentioned, extremely unselfish act of Saul was judged as disobedient by Samuel and declared his judgment: “Jehovah will choose another person to be king over Israel.” (1 Samuel 13:14) What else is needed to turn a good person into bad?
With Saul, this was a part of his arrogance. He assumed because he was king of Israel that he also had the priestly authority to offer sacrifices. It was for his arrogance and his tendency to second guess the Lord. Just as he did a short time later in sparing Agag and the livestock of the Amalekites, which showed he didn't learn a thing from his earlier disobedience.
Just as when Aaron's sons thought to use "strange fire" in their offerings, it was a contempt for the word of God. Based on the language used in 1 Samuel 13, we know that Saul did not obey the clear commandments of the Lord. Nowhere had Saul been ordained to the office of priest, nor was he of the necessary tribe to receive that office. This is one reason the Protestant reformers denied the priesthood authority of the Roman Catholic Church. Constantine may have been the emperor of Rome and the most powerful ruling authority of his time, but he lacked the authority of a single elder or bishop. It's also the reason the Pope excommunicated the bishops and King Henry VIII because he, being king, did not hold ecclesiastical authority. (Yes, it was an irony, but such is history.)
In short, there was no reason to think that Saul had any right, despite his intentions, to proceed with the sacrifice. If he grew tired of waiting for Samuel, why didn't he command his own Levitical priests to offer the sacrifices? Whatever made him think that he, lacking the priesthood, could offer them up? I suspect the priests followed Samuel's orders, not Saul's, but remember Uzzah, who reached out to steady the Ark. They had not secured the Ark as the Lord had required and when the oxen stumbled, Uzzah, lacking authority, attempted to steady it.
Saul knew these stories as well as we do and he knew it was a grievous sin to take authority that had not been given him. This is why Samuel became furious on both this occasion and the one with Agag. In our day we're trained to look at motivation when deciding what's right and wrong. But in Samuel's day, they took things like this far more seriously.
Having said that, the Governing Body have no authority, either. They are part of a manmade church with manmade policies that belie the merciful nature of God. Had Saul acted in good faith and not known the seriousness of what he'd done, the Lord would have been unjustified in his actions. The practice of shunning and disciplining church members is a policy that they are unauthorized to make.