Your points are well organized and I tend to agree (especially that there would be an easier way to get rid of him), but I don't think you'll stop those that see a conspiracy around every corner.
I tend to see our government (today) as a very mismanaged large corporation. There are people over-reaching and those above them are trying to hide the damage and spin the conversation.
What matters is what happens after Mr. Hastings' death. If the FBI is to be trusted, they will deny involvement on the low and the high: a trustworthy organization does not want to create even the slightest perception that they would kill a journalist. A trustworthy organization does not wish to instill fear in Hastings' colleagues. If, however, the FBI is not to be trusted, they will spread rumors that they are responsible: even if they did not kill him, it benefits them that journalists would be nervous to investigate them. This was the tactic of the KGB in the Soviet Union: they would stoke rumors of their ferocity by claiming responsibility for the otherwise-natural deaths of political contrarians.
What is truly to be feared is not that the FBI killed Michael Hastings, but that the FBI would like people to believe they killed Michael Hastings. Therefore, a rational yet paranoid individual might suspect sage_joch of being an NSA provocateur, but not Taylorious. That is the sort of corruption that will send a country into the dark ages for a century.
Uh, name a few?
[citation needed]
I don't know, I think the US government seems pretty ruthlessly efficient at toppling Middle Eastern governments, transferring wealth from taxpayers to big banks and large corporations, increasingly centralizing power into the federal government and large corporations, and breaking down families and increasing reliance on the state. And spying on it's own citizens.
I suppose, if you automatically dismissed any such thoughts to the contrary as "ridiculous conspiracy theories", it could look like it is all a problem of mismanagement. Maybe.
I only say this because people often talk about that as if the reporter had done deep black ops to gain covert information, thus making enemies throughout the establishment, when in reality he simply reported quotes directly fed to him, and in some ways acting on behalf of the establishment.