I quite agree that Gibbon was anti-Christian, attributing much of what went wrong in the empire inappropriately to Christianity while at the same time ignoring its beneficial effects.
However, I still don’t understand why a comment about all but Claudius of the first 15 emperors having non-het tendencies is somehow an attack on the Pope or Catholicism. For most of this period, while there may have been a Bishop of Rome around, he certainly wasn’t a Pope, and Protestants equally claim these early Christians as their forebears.
To address the actual issue, the first 15 gets us down thru Hadrian, depending of course on how you count them. (Do you count the first three in the Year of the Four Emperors?)
Anywho, the Julio-Claudian emperors are five in number. All but Claudius were either well-known or rumored to have male lovers.
The Year of Four and Flavians: 6. A very little research indicates all but Vespasian and Titus were light in the loafers, and I can’t really find info on them. Both were well known to be fond of women, though.
Nerva, Hadrian and Trajan complete this 15. All three, especially Hadrian, were well known to like boys. It is perhaps indicative that while all three married, none had children. Hadrian made his dead lover a god throughout the empire.
So that leaves us with no more than three of the 15 being entirely correct in their affections, with questions about two of those.
Of course, the historians may have lied about some of these men, but during this period referring to a man’s sexual encounters with males was obviously not very successful as a slur, with at minimum 12 of the first 15 having them.
Compare our presidents. AFAIK, the only ones who had rumors about him along these lines were Buchanan and Obama. That’s two (possible) of 43. I don’t personally take the Obama allegations very seriously.