I’m not sure why you disagree with me. I was disagreeing with the author and therefore agreeing with you.
As with the deaths of most civilizations, classical civilization was nor murdered, it committed suicide. The major cause was several centuries of civil wars, caused basically by the Roman failure to ever develop a basis for legitimate rule and especially for succession.
Anyway, the decline and fall of the Roman Empire has been a source of after-dinner discussion for at least 400 years..... it certainly exhausted Edward Gibbon, who died only two weeks after he finally saw it in print.
Michael Grant pushed taxation as a cause. Others like trade imbalances with India better (depletion of cash in circulation) .... and of course some people blame Christianity, or the reorganization of the Roman army, or what do you like.