Really now… where does it say that in the Cathecism? I think there is a big difference between actual sin and near occassion of sin. One can accidentally put themselves in a near occassion of sin without even being fully aware.
If its accidental and then when you’re aware and remove yourself right away, there’s no sin. But voluntary proximate occasion of sin is a mortal sin
I don’t know if its in the new Catechism, but its an element of moral theology and you can read about it in the Catholic encyclopedia, moral theology manuals I guess, and more detailed examinations of conscience such as this one
catholicapologetics.info/thechurch/sacraments/adults.htm looking at obscene books/pictures is listed under “mortal sin” here.
From Catholic Dictionary:
"OCCASION OF SIN
Definition
Any person, place, or thing that of its nature or because of human frailty can lead one to do wrong, thereby committing sin. If the danger is certain and probable, the occasion is proximate; if the danger is slight, the occasion becomes remote. It is voluntary if it can easily be avoided. There is no obligation to avoid a remote occasion unless there is probable danger of its becoming proximate. There is a positive obligation to avid a voluntary proximate occasion of sin even though the occasion of evildoing is due only to human weakness."
catholicculture.org/culture/library/dictionary/index.cfm?id=35228
From the Baltimore Catechism:
. 771. What do you mean by the near occasions of sin?
A. By the near occasions of sin I mean all the persons, places and things that may easily lead us into sin.
Q. 772. Why are we bound to avoid occasions of sin?
A. We are bound to avoid occasions of sin because Our Lord has said: “He who loves the danger will perish in it”; and as we are bound to avoid the loss of our souls, so we are bound to avoid the danger of their loss. The occasion is the cause of sin, and you cannot take away the evil without removing its cause.
Q. 773. Is a person who is determined to avoid the sin, but who is unwilling to give up its near occasion when it is possible to do so, rightly disposed for confession?
A. A person who is determined to avoid the sin, but who is unwilling to give up its near occasion when it is possible to do so, is not rightly disposed for confession, and he will not be absolved if he makes known to the priest the true state of his conscience.
Q. 774. How many kinds of occasions of sin are there?
A. There are four kinds of occasions of sin:
Near occasions, through which we always fall;
Remote occasions, through which we sometimes fall;
Voluntary occasions or those we can avoid; and
Involuntary occasions or those we cannot avoid. A person who lives in a near and voluntary occasion of sin need not expect forgiveness while he continues in that state.
Q. 775. What persons, places and things are usually occasions of sin?
A.
The persons who are occasions of sin are all those in whose company we sin, whether they be bad of themselves or bad only while in our company, in which case we also become occasions of sin for them;
The places are usually liquor saloons, low theaters, indecent dances, entertainments, amusements, exhibitions, and all immoral resorts of any kind, whether we sin in them or not;
**The things are all bad books, indecent pictures, songs, jokes and the like, even when they are tolerated by public opinion and found in public places.
**
ourladyswarriors.org/faith/bc3-18.htm