When our focus is set on the Spirit of Jesus (v.6) it is sin (separation from God) that we will condemn, not people. God yearns intensely for the people He created and condemns the separation and lies that keep them away from Him.
To walk according to the flesh is to set our minds on believing the lies Satan has implanted in us. The inevitable result is hostility toward God at our gut level, even if we pile on mountains of piety, religion, good works and Biblical knowledge. It only buries the lies deeper. And like fossils in the ground, the more weight you pile on top of them the more they turn into fuel for fire. Sooner or later they will ignite in rebellion and hostility toward God and all who are like Him. We are storing up wrath for the day of wrath.
The only solution is to acknowledge our root lies through the ministration of the Spirit and let Him replace our foundations with truth. Truth, most of all, is truth about who God is, what He is like, how He feels about us. Every lie at its root attacks God's reputation and only God Himself can address and change those fossils in our heart.