Mazal tov! What exactly are we celebrating?

This past Monday, Mussie and I were blessed with our fourth child. A beautiful healthy baby boy, thank G-d.  
Moments after his birth, one of the nurses put an ankle bracelet on my son. We were told that should anyone try to remove the infant from the floor, the hospital would go into automatic lockdown, alarms would buzz, the GPS tracker would tick and the police would be there instantly. Unfortunately, this is a necessary precaution.
What a grand welcome, I thought, for this precious newborn who just left the comfort and safety of his mothers womb, and emerged into the world.
This is the reality of the world many of us see.
Yet, when the newborn arrives there is so much joy. So much happiness, so much excitement, despite what this pure child may have to face. And the question begs itself to be asked, “why is there such a celebration at birth?”
Also, are we even sure the child will grow up and live a meaningful productive life and not Heaven forbid the opposite?
Perhaps only after someone has accomplished something in life, or once their life is complete, can we evaluate and honestly determine if their life should be celebrated and lauded. Why are we rejoicing on day one?
At the core of the Torah's vision for life is the idea that every individual human being has a soul—a distinct spiritual identity, and a distinct mission in life.
This is what comes into being the day the child is born. Not simply our physical existence, or our vitality, and not even just our potential—which can go either way. The fetus exists, is alive, and feels, before being born as well. But birth marks the point at which our body is fused with our own unique soul, the point at which we attain our independent individuality.
Chabad philosophy explains that a birthday is the day G-d says that "You, as an individual are special, unique, and utterly indispensable. No person alive, no person who has ever lived, and no person who shall ever live, can fulfill the specific role in G‑d's creation entrusted to you."
So as soon as the child is born, it is time to get to work. There is a specific reason he was born, and he must do his part in making this world better. The fact that another team member joined the workforce of billions tasked with perfecting G-d’s world is a reason for all of us to rejoice.