You have to look at this from the evidence. What really happened? Thomas Sharp stirred up a bunch of militia men to murder Smith. This was because of political disagreements. Sharp could care less about Smith's beliefs, only as he could use them against him. All of those who were believers, like the Laws, Higbees, Cowles, etc. were working to change things from within. JOSEPH expelled them. So then they were forced to work from the outside. They were not involved in the murder. Those that were, were goaded by those like Sharp, whose objections were political in nature. Law claimed he wanted to "tread on the viper", but never advocated violence. That is all Sharp was advocating at the last. Where did the evidence lead? Who was brought to trial?
An eyewitness to the murders, Jeremiah Willey, said that John Wills, Gallaher (a man whose first name has fallen out of the historical record), and William Voras were among the men that broke into the jail room. Willey reported that Gallaher shot Joseph Smith in the back as he ran to the window. Wills, Gallaher, and Voras all received wounds when they were shot through the cell door by Joseph Smith. In the end, just five of the nine indicted men would face trial: Levi Williams, Thomas Sharp, Mark Aldrich, Jacob Davis, and William Grover.
http://famous-trials.com/carthrage/1262-home
In vain, the Mormons tried to link Church dissenters to the murders. They even tried to implicate Joseph H. Jackson, and all later Mormon historians have is hearsay to do so. There is no evidence linking any Church dissenters to the murders. All of it points to Sharp and those that he duped into going and committing the murders, which was because of political motivations.
Did religious matters get Joseph to Carthage? In part, YES. But was that the reasoning behind the murders? No. It was all about opportunity, and Joseph and others like Sharp, knew he would be vulnerable there. (To be convicted of something). But even Joseph did not think he was going to be murdered when he surrendered.