The field is the world not the church (Matthew 13:38). The children of God are sown into the world as good seed. When we look at all the instances where it is mentioned, we discover that the kingdom of God refers to both the King’s dominion, which is all of creation (and where it is sometimes questioned, for now), and His special domain that His children are under, and will be “in” when in heaven, and where His reign is not questioned, the church.
When Christ comes again He will separate the wheat and the weeds, the sheep and the goats. God allowing both to grow together means that the weeds, the goats, are not finally judged yet. The wheat and the weeds live side by side in a composite human society, for now, and God’s people live as a subset of that, until Jesus comes again. Christians are in the world but not of it. They are not supposed to try and dominate society or isolate from society.
Wheat and weeds together doesn’t mean we must let them grow in the church but in the world. Having said this, in the church we might not know if a person is a weed at first. However, the nature of a weed is that it wants to overrun the good ground. A reliable measure is that when you give a person power you will see who they are come into focus. Many of our troubles come because we elevate a person who is a weed into a leadership position and they lose a sense of humility after a while. They feel like money or power entitles them to do what they want without reprise, extra room to be obnoxious. Eventually their real self comes to the fore (1 Timothy 5:24). Then we see the weed as it is.