Sin is in the heart and mind first before it becomes an action. If it were merely physical, as the Pharisees taught and practiced, then it would be a matter of cutting off an arm or gouging out an eye and not sin. Since it's the HEART and THOUGHTS that are the problem, we need to get rid of the OLD HEART and have a NEW ONE. That means we need regeneration in order to see our sin as GOD sees it and seek His forgiveness and salvation. And that can ONLY be done by God Himself.
Eze 36:22 "Therefore say to the house of Israel, 'Thus says the Lord GOD, "It is not for your sake, O house of Israel, that I am about to act, but for My holy name, which you have profaned among the nations where you went.
Tit 3:5 He saved us, not on the basis of deeds which we have done in righteousness, but according to His mercy, by the washing of regeneration and renewing by the Holy Spirit,
So whether you're talking about shooters, pornography watchers, or Islam's burkas for women (because it's "their fault" the men lust), God is NOT a God of reductionism. Rather He is one of precision:
Heb 4:12 For the word of God is living and active and sharper than any two-edged sword, and piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart.