There is no such thing as a victimless sin. Every sin is contrary to the will of God as expressed in Scripture and Church teaching. If one pursues the theological threads, one finds a rational basis for even seemingly “arbitrary” proscriptions. It’s a package deal of Truth ultimately grounded in God’s greater purpose for Creation and for Man, including each individual man or woman.
The necessity of obedience to the will of God who created me for a purpose is reflected and extended in obedience to every dogma, obligation and proscription. Any disobedience is ultimately a sin against God — hence, there is always a victim. But the purpose of each creature’s life is also God’s will — so each sin I commit that does not directly harm another creature has me as its creaturely victim. Hence, every one of my sins has at least God and myself as victims.