Finkelstein - The WTS. leaders/ GB associate the originating pagan practice of celebrating birthdays of pagan gods , which was true in ancient times as a form of imposing idolatry .
Now days in are modern times its a more of practice of love, appreciation and respect.
ie. a child's first birthday or a celebration of someone turning 100 years old.
This really isn't idolatry or idol worship in premise.
The problem with Jehovah's Witnesses—as with most Christian denominations—is that they think that the Bible is still applicable today. It's true that some teachings are; however, that is not true of most of what you can find in the Bible—or in the early Christianity, for that matter.
The authors of the Bible books were simply men who adhered to the cultural norms of their time. For instance, when Origen and Tertullian wrote against birthdays, it was because the early Christians (their culture) were scared—even terrified—of paganism. This goes back to the fourth, third, and second centuries BCE when the Jews began to see what influence the Greek culture had upon the Jewish customs. The Jews became scared of paganism—including the Hellenization—and that also affected the first Christians who were Jewish. And so the early Christians were afraid of anything even remotely pagan. This is why you have Paul saying that men should not have long hair: fear of paganism. It's simple culture affecting religion, and people can't see that.
Today our culture is not afraid of paganism. This is why churches that apply modern standards to their policies and rules are not scared of birthdays, Christmas, Easter, etc. They don't read the Bible and see it as a guide for all eternity. Some Christians, though not many, have learned how to differentiate between God and culture. Jehovah's Witnesses still have a long way to go.