Because we are a People and this is how we are defined.
You don't get to define anyone but yourself.
What happened to all that stuff about religious freedom you were talking about before? Have you decided to abandon that?
Circumcision is part of our covenant. We don't choose for that to be true. We are born into that truth.
A child who isn't even aware enough to understand that his limbs belong to him certainly doesn't have the requisite understanding to enter into a covenant.
You might as well complain about why you are born with blue eyes or type O blood. As a Jew, there will be circumcision in my family. It's simply part of being a Jew.
You're equivocating. If you're talking about the heritage you're born with, well, you're born with it. A child's heritage, family, and cultural history is what it is regardless of what anyone does to his genitals.
If we're talking about the results of human choices, then we're talking about something other than just heritage.
My parents didn't choose my blood type or eye colour. They didn't deliberately intervene to choose them and they certainly didn't try to intervene to choose my religion.