Thomas, I believe mingling with worldings for the sake of leading them to Jesus is a worthy model. But it must be on Jesus' terms. I agree with Paul's counsel of concern. We need to be very careful in ministering to worldings that in the process they do not lead us away from Jesus.

Paul, as a good shepherd, jealously guarded his flock. He often counseled church members to avoid [1] hypocrites and [2] heretics and [3] people who reject the gospel as it is in Jesus. "And if any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed. Yet count him not as an enemy, but admonish him as a brother." (2 Thes 3:14, 15)

1 Corinthians
5:9 I wrote unto you in an epistle not to company with fornicators:
5:10 Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world.
5:11 But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.

2 Corinthians
6:14 Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
6:15 And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?
6:16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in [them]; and I will be their God, and they shall be my people.
6:17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean [thing]; and I will receive you,
6:18 And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty.