Tradition is the democracy of the dead; it is applying the votes of our ancestors , cast long ago and in different times, to our present circumstances. Circumcision is traditional.
Whichever Jew did the first circumcision must have been uncircumcised . Some committee of Jews or proto-Jews (Jew as religion rather than a people) or their appointed leader, decided that, henceforth,every boy was to be circumcised. Why? Did they circumcise themselves? It must have had some logic then. As sir.prize says health and hygiene seems the reason, just as the dietary laws were for health. Pork, shellfish and other forbidden foods are all risky to eat; they can still be.
The original reason is long forgotten and the practice becomes identified with the religion and then treated as an identifier and article of faith which unifies a 'nation' or religion and has non-observers treated as outcasts. It is as though we still followed archaic laws here, laws which were necessary when passed and had some logic behind them, instead of ignoring them and having a Commission which identifies them and has them removed from the statute book.
This is reminiscent of the docking of dogs' tails as a controversy. Those for were ardent in their opposition, citing tradition to justify docking the tails of pups of poodles, spaniels and other breeds. It was an article of faith for the breeders; itwas tradition, the dogs looked right. It had no logic, save, conceivably, to stop gundogs that were employed to go into thickets from being deterred by fear of injury to the tail or suffering such injury.
Circumcision is in the same category . It has no logical or practical purpose any more and should be prevented.But it won't be.