One of the claims of the Catholic Church is that we hold the Deposit of Faith in its entirety, as much as was revealed by God, and the authority to proclaim, teach, and protect it. And so anyone who is outside of it might well be participating in the life of Christ, thus making him or her a Christian; even so, without being a member of the Catholic Church, that Christian is living a life that is lacking.
For a Catholic to not rejoice when one enters the Catholic Church and not have sadness when one leaves is to deny that we have that fullness. It is about Christ, because we not only desire all to have Him, but to have Him in His fullness.
For a Catholic to not rejoice when one enters the Catholic Church and not have sadness when one leaves is to deny that we have that fullness.
Granted. If you believe you have that fullness and others lack it, I can see your point. Though I reject completely the idea that a Protestant, simply because he is a Protestant, doesn't have this fullness. (What a tragic view of your fellow members of the Body!) Besides, I know too many faith-filled Protestants who are living the fullest of lives in Christ -- and are being used by him in amazing ways, far beyond what most Christians, including Catholics, could ever conceive of. I wouldn't dare to say they're "lacking."
But what I often see here are phrases like "welcome home" used as a slap in the face to Protestants reading a post rather than as a genuine welcome to the new Catholic a poster is addressing. I see it used as a weapon more often than not.