Right. Comes from a teaching that “these X,Y,Z things/actions/thoughts are bad *in and of themselves even if nobody gets hurt *”.
Now, it’s true, all of Christianity is supposed to believe that about any number of “sins” – you should not lie, period, even about taking a sick day for other reasons, for instance – but in the American cultural environment of the last century, there was a visible contrast between how that was handled among the Catholic and the secularized-Protestant group that dominated society.
Protestantism believes in Salvation by Faith, which to many in American society became simplified into: you Repent and Accept Jesus and that’s it, no need to dwell on what you did before, just stop active sinning, live a law-abiding life, show up for services and tithe, and you’ll be fine. An ocassional little-white-lie for a “good reason” or moment of self-indulgende could be covered under the divine mercy if it did not affect the Big Picture.
Simultaneous to this, a large segment of the population became completely secularized or adopted new forms of spirituality where utilitarian/humanistic ethics were the norm. In this POV, if the action did not really hurt anyone, it was not really bad; and the thought alone was hardly ever ranked as “wrong”.
Meanwhile Catholics had a very noticeable set of other Church-specific precepts to hold to [e.g. no meat on Fridays, civil weddings not good enough] and Sacraments to participate in periodically, lest you become the metaphysical equivalent of an uninsured driver. The little-white-lie or the moment of self-indulgence were things you had to remember to confess next Saturday, and you’d be doing penance for them in order to reflect upon your weakness and see how you can keep from getting into that situation again.
Thus to the “mainstream” , persistent or recurrent consciousness of what have they done/said/thought wrong or just failed to do/say/think exactly right was neurotic, while to the Catholic it was essential to spiritual maintenance.
Problem is, many of our parents/teachers did not bother to explain beyond “that’s bad to even think about! You’re contributing to Jesus’ pain! Think of St. Precarious of Myrna, who had weasels rip his flesh rather than stay home from Mass!” and that made a lot of us neurotic.