Actually the fall of Rome is directly connected with the constant migration of nomadic peoples who were being displaced and forced westward. Once the Roman Empire took on a defensive posture, it became inevitable that it could not hold back the constant and changing threats. A simple explanation, but then it is generally considered probable. Dark Lord Revan you might find it interesting to note that one of the first noteworthy treatise on the subject - written by Edward Gibbons - had a love hate relationship with Chrisitianity.
Many people have contended that what actually held the Empire together for so long was the growing influence of the church and the adoption of church structure into the day to day governance of the state. In the end, however, it was more due to a system that could not afford its defenses and opted to decentralise authority, until the local municipalities had to bear the load that had once been centralised. Furthermore, the Roman Empire - proper if you will - survived well into the 15th century CE. And the only reason that Constantinople fell - some argue - was not due to gluttony - it was due to the Crusades that the Papcy used to justify the conversion and recapture of the Holy Land through bloodshed. I won't debate the interpretation, only to point out that it was not until the 12th century that the Eastern Empire - for lack of a better term - began to have to defend itself on two fronts.
On the western with the Papacy economically and eventually physically, while the east held the growing Muslem states and principates. Finally, if anything or anyone brought Europe out of the Dark Ages - again for lack of a better word - it was Arab and Islamic scholars who advanced Greek and Roman learning for some 1000 years while the Church imposed a feudal system that only kept any learning alive in sequestered and very remote monestaries - particularily Scottish and Irish, that were really more scholarly than they were theological. Well there is some more socio-historic background.
Note: I am not sure where the idea has arisen that someone is arguing that it would have been better if Jesus had not existed is arising, but I can assure you I would not make such an argument, fwiiw.