Apostasy, anyone?

Steve Shiffrin's recent post got me thinking, and, alas, there is no way to raise this question without seeming quaint, stupid, or snarky.  But why isn't the answer to the question, "Why don't I leave the Church?", this one:  "For a person baptised into the Catholic Church to leave is to commit the mortal sin of apostasy"? To be sure, if the Church is flawed in such a way as to justify one's "departing," then one hardly need worry that there is such a reality as "sin" (and its consequences) as understood by the Church.  But on the tenet, which I accept in faith, that (as I sometimes hear when travel brings me to parishes with loquacious celebrants of Holy Mass) "It is God who gathers us together as Church," can there possibly be a reason to undertake to "leave" the Church?

I am always impressed when I hear from theologians and others who feel wronged by the Church or the magisterium that they do not see leaving as an "option."  Their steadfastness to the reality of the Church gives credibility to their stuggle with holding what the Church teaches.  Of course, when the struggle ends and the defined faith is rejected, then one has already put oneself outside the communion that is the Church, though without the power to remove the indelible mark of baptism.