All sin is deadly and separates us from God. There may be different levels of consequence temporally but all sin eternally condemns us.
Why? You break one part of the law, you have broken all of the law. Thus saith the Lord.
The first sin that cast all of mankind into sin and turned all of creation into a fallen world was because two people disobeyed “Don’t eat this one thing.” Not very demanding or particularly wicked, many of us have disobeyed parents and eaten a sweet or snack when we were told we could not have one. The consequences are not on par with what a murderer receives, yet for our first parents it broke God’s perfect creation and separated them spiritually from God, with no power of their own to make things right.
All sin is telling God, explicitly or indirectly, “NO, I will do what I want, not you, God!” And therefore all sins, no matter how small, while not equal in scope, or intent, or consequences, are deadly because breaking any infinite law of God requires an infinite penalty be paid. All sin is rebellion against God, at its core. Which is why we believe Christ’s atoning sacrifice paid for all our sins completely.
Of course, God Knows the time of our sin, what the sin is going to be, and the consequences of the sin, beforehand. Right?