Totalistic faith

Perhaps the primary Catholic objection to the Protestant faith is doctrinal diversity within the Protestant tradition. However, that has a fringe benefit. Catholicism is totalistic. "We're the One True Church®". 

The danger is that you have lapsed Catholics who believe the arguments against the Protestant faith, but cease to believe the arguments for Catholicism. So they land in atheism. There's nothing in-between. The next stop is the last stop. 

That's a risk for deconversion in general. Many people use their provincial personal experience as the benchmark. Whatever religious tradition they were raised in supplies the standard of comparison. If that's totalistic, it makes atheism the fallback position, viz. lapsed Muslims and Mormons who become atheists. 

If you continue to believe half the arguments of the Catholic apologist ("The Protestant faith is wrong!"), but discontinue believing in the other half ("Catholicism is true!"), then there's nowhere else to go except atheism. A possible exception is Eastern Orthodoxy, but disillusionment with one high-church tradition is apt to leave one skeptical about high-church traditions generally, since the many of the arguments are parallel. 

By contrast, Protestantism many alternatives within the Christian paradigm. You can go from paedobaptist to credobaptist or vice versa, cessationist to charismatic or vice versa, amil to premil or vice versa, young-earth creationism to old earth creationism or vice versa, freewill theism to Calvinism or vice versa, sola fide to NPP or vice versa, &c. In that respect, the Protestant tradition has more give than Catholicism. 

At the same time, this also illustrates the need to present the adherent of a false faith with a constructive alternative. Both conversion and deconversion are paradigm-shifts. We need to offer them a different theological paradigm. 

In their fanatical myopic zeal, Catholic apologists back Catholics onto a ledge: either come inside or jump to your death! If a cradle Catholic has been conditioned by Catholic apologists to believe that Protestantism is not a viable option, then their only remaining option is to jump from the 10th floor window to the atheist pavement. Catholic apologists labor to discredit any other theological option. So it's either Catholicism or Christian suicide. There's no safety-net.