Christians often find themselves stuck between a rock and a hard place when it comes to loving people that don't yet have a relationship with Jesus.
On the one hand, we want be a witness of the power of the gospel to transform lives and the love of Jesus for everyone, even non-believers. On the other hand, we don't want the world to tempt us and influence us to lose our focus on Christ. For many followers of Christ, this creates an internal anxiety that causes confusion, conviction, and even spiritual schizophrenia. How can we reach lost people without getting close enough to know them and love them? But if we get too close, what if they rub off on us and drag us down?
This is a false dichotomy. It's not like sinners have the flu and we'll catch it if we get too close! If you are grounded in the Person of Christ and the Word of God, and you understand your mission of being a representative of the gospel to the world around you, not only will you not be afraid of people who are different than you; you will actually be drawn to them in hopes that they can see the hope of the gospel through your life and your words.
Of course, this doesn't mean that you should adopt their worldview, get drunk or high with them, or buy into their lifestyle. Stand firm, with humility, on your convictions as a Christian. Become an influence in their lives for good and for the gospel and resist any negative influences that come your way. But please, for the sake of the Kingdom, engage people who are far from God with sincere love and care. They are image bearers of God, just like you. They are also sinners, just like you. The difference is that your sins are forgiven. God can forgive and redeem them, too, and He wants to use you as His ambassador.
So what should we do with 1 Corinthians 15:33? "Do not be misled. Bad company corrupts good character." Paul was speaking to a specific situation where some so-called believers were arguing that there was no resurrection from the dead and that even Jesus had not been raised. In that case, Paul warns them to contend for the truth of the resurrection and refuse to be swayed by a false teaching. There comes a point where it's useless to argue with someone that you know cannot be convinced by your words. When that moment comes, if may be time to separate from them or to refuse to entertain their false teachings. Paul admonishes Christians to keep being a witness while refusing to be swayed from their faith.
We can follow that same advice while living boldly out our faith in our relationships with those who don't yet know Jesus. You can't reach a people group while attempting to avoid them. You can't be witness to lost people if you never meet or talk to any lost people. Step out in faith, trust the Spirit inside of you, stand firm on the Word, and get to work. There's a big world waiting for the good news.