The fall of Rome came as result of combination of heavy decentralization and external pressures. Basically, due to the fact that the empire was so large it required a lot of administrators. In the Republic and during the Imperium leading up to the the 2nd to 3rd centuries this worked out fine, the people in charge were generally effective and had the good of the state at heart. However, nearing the end, wars of succession depleted the armies of the Empire and the administrative authorities were weak. The combined outside threats of barbarians and, as you said, Christianity (and specifically Christianized barbarians), played massive roles in destabilizing Roman territorial control.  Roman society depended heavily upon its pagan religious beliefs and it legalism. Paganism was Rome, Rome was founded upon it, and the pressure of Christianity called into question the very nature of Rome. So, you are very much right. People will blame gays and trannies for anything, even if they were never significant at any point during history.