Do you know WHY they were against doing an autopsy? Could be anything, from belief they already know why he died, to trying to protect his legacy, to simply being in shock, to something more sinister. Seems to me, if for no other reason to prevent just these types of discussions, an autopsy would have been ordered.
Further, the autopsy should include a team of forensic specialists, and should be trustworthy beyond question.
.
Do you think that the conspiracy types are going to believe an autopsy that tells us the overweight, 79-year old, cigarette-smoking Associate Justice died of a heart attack?