I have no problem with believing in massacres committed bt ancient Hebrews (the Bible has plenty of them), but my ability to believe is stretched by whole "licking up the blood" thing.
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It seems to me that Gibbon's main point is that there was an often brutal struggle between Nazarene (primitive Christian) and non-Nazarene Jews and also, more broadly, between the Empire and Jewish revolutionaries.
These struggles, we're reasonably encouraged to believe, led to cycles of violence and a severe frame of mind which explains the various ancient periods of persecution.
Also, reading Gibbon tends to make you write, if only for a short time, like Gibbon: or as near as you can manage.
.d.