Had a long discussion over the weekend with a family member, a practicing Catholic, who doesn't believe in any sort of eccelestical infallibility. She said in order to do so that would require her to believe that she is going to Hell, along with most of her children, for the use of contraceptives. Definitely an impediment, I would have to say, a powerful incentive to believe the Church errored. I explained the conditions of what was required for a sin to be mortal though I recall explaining the same thing before. For her, the Church's credibility was shot during the '50s when what she considered non-grave matters (i.e. eating meat on Friday or missing Mass) were mortal sins.
I asked her why it was there were no "bad Catholics" anymore, how we now simply change the standard if we can't meet it, but admittedly it's one thing to call oneself a bad Catholic, it's another to feel that should we suddenly die, without contrition or Confession, we would go to hell. Perhaps previous generations lived constantly on that precipice, with portions of their lives lived in alternating states of mortal sin and post-Confessional grace. I suppose that would appeal to risktakers and daredevils.
But this looks at the question wrongly of course. Here's a paraphrase of a Scott Hahn talk:
This image of law as limiting our freedom is in the water now, it’s in the air. The concept of mortal sin leads to the “via moderna”, the modern way, in that it makes us more slave than child, making us aim to avoid punishment rather than love. Pope John Paul II said, “Sin affects our intellect by exchanging a vision of God as Father to one as master.” That God's laws are for our personal fulfillment is mostly foreign to us because the last seven centuries have made law the opposite of freedom and personal fulfillment.