This point is always brought up as ding on Catholics who move to the Episcopalian Church.  It is the Catholics moving into the Episcopalian Church that keeps the numbers from being even worse.  The stats on Catholics leaving the Catholic Church are much higher, especially among whites, and in the last ten years or so, the exit doors have opened wide for Hispanics moving to the Evangelical Churches.

All organized Christian religions are losing membership in North America.  Even the LDS Church with it's relentless missionary activity is losing membership in North America.  I suppose some people would attribute this loss to secularism, but I also think it's a cultural rejection of religious authoritarianism.