I know how you feel. It is very easy to see the corrupt nature of sins which effect other people directly. The solitary sin is easily hidden by a corrupted conscious. We know that God’s will is much more than just not hurting others. It involves our thoughts, our words, what we do and what we fail to do.
As was stated, the corruption of our conscious is an effect of the sin itself. The corruption takes place on an individual as well as a collective basis. Repeated individual sin, and the more that society sins, the more disorder occurs in our lower faculties.
The sin leaves a residual habit upon our spirit. It becomes a vice. We can confess the sin and the sin is forgiven, but the effect of the sin remains. A way to overcome vice is through virtue. Mortification is also helpful. Lust and Gluttony are related to the same lower faculties. Fasting can help to overcome lust. Grace is designed to help us overcome sin. Sacramental grace is one of our best tools. Through the sacrament of confession, actual grace is given to overcome the particular sins that are confessed.
Overcoming lust is a real battle. The stakes are high.
AND - here is my own opinion without much biblical support or any church teachings.

During the sermon on the mount and when Christ spoke about adultery, He taught us that thoughts were just as sinful as actions. Why is that? It seems counter intuitive. Doing something must be more serious than just thinking about it - Right? My guess is that the spiritual world does not include physical senses as we know them. Our actions are not “seen”, but only known by the thoughts that have to accompany them.