I haven't been able to get through all the previous posts, and I am not an expert, but everyone is entitled to an opinion, and here is mine.
The WT maintains that the divine name was pronounced in the first century and was pronounced by Jesus and apostles. They maintain that the practice of pronouncing 'kyrios' or a substitute word came in after the first century. To support this they point to existing early copies of the LXX which contain the tetragrammaton in Hebrew characters, embedded within the Greek text. To me this is actually evidence against their position, and indicates that the copyist thought the tetragrammaton so sacred that he had to reproduce it unchanged and untranslated. One of the early church authors, I forget which one, even commented on how some people reading the LXX would pronounce the word 'pipi' because the Hebrew tetragrammaton letters resemble the greek letters pi,iota, pi, iota. So I think the evidence does not support the WT view, but rather supports the prevailing belief that pronunciation of the divine name ceased much earlier, in the couple of centuries B.C.
So it follows that inserting the Name in the NT is presumptuous and simply wrong. It would be different if there were even one NT copy that had the Name, but there isn't (so far).