I don't think it was Christianity or religion in general that led to the fall of Rome, at least not in the sense that it led to the abandonment of science. It had more to do with Rome's over extension both militarily and economically. General decadence among the ruling class probably didn't help. It made them ripe for invasion and that's what happened....repeatedly. These invaders were generally less culturally and scientifically advanced and that's what Rome became.