Although we are to love our enemies and pray for people who intend to do us harm, we do need to be cautious regarding those we trust as close friends:

A righteous man is cautious in friendship, but the way of the wicked leads them astray.
Proverbs 12:26

Too late some have discovered that "friends" from the Internet cannot be trusted. Children especially are vulnerable to be taken advantage of by people they meet online. False friends can insinuate themselves into our lives even in "safe" situations, such as work or church or social clubs of various kinds. Being friendly with others does not mean we should be quick to put trust in a new acquaintance that is not earned.

Israel was warned to not follow family and friends into worshiping other gods. As a nation this warranted a death penalty (Deuteronomy 13:4-11) as treason would in nations today, but Christians are not given this authority; our role is one of modeling a life of faith in and obedience to God (2 Peter 3:11-14).

Jesus warned his disciples to watch out for false prophets and not fall for their lies (Matthew 7:15-16).We also must watch out we are not persuaded by friends we have trusted to follow them into activities or philosophies which pull us away from God's loving instructions for our good (Proverbs 1:8-19).

True friends will warns us if they see us making choices which are not good for us or others:

Better is open rebuke than hidden love. Wounds from a friend can be trusted, but an enemy multiplies kisses.
Proverbs 27:5-6

If we are a true friend, we also have a responsibility to the friend to say, "Stop", or "Don't" along with some information and helpful support to make that change possible. We all need at least one friend who can talk us down from the edge of ruining our lives with sin. This isn't about nitpicking personal irritations or annoyances; this is about pulling a person away from destroying his or life.

What sins are important enough to put your friendship at risk over? Unhealthy relationships, either romantic or law breaking; unhealthy addictions such as gambling, alcoholism, or drugs; unhealthy attitudes such as holding onto anger and grudges and planning revenge---whatever will cause harm to your friend and others is important enough to speak up even though it is uncomfortable and hurtful to you and your friend.

This type of intervention is between friends, not a call to confront co-workers or acquaintances or strangers on the street. We are cautioned to be careful when we do this:

Brothers, if someone is caught in a sin, you who are spiritual should restore him gently. But watch yourself, or you also may be tempted. Carry each other’s burdens, and in this way you will fulfill the law of Christ. If anyone thinks he is something when he is nothing, he deceives himself. Each one should test his own actions.
Galatians 6:1-4

Close friends are essential to our emotional health. Friends who stand by us through thick and thin are to be treasured and cherished. Be cautious about who you allow in that inner circle of friendship. Make sure those you let close can be trusted. Be a good friend who not only affirms, but is also willing to correct a friend who is slipping away into a harmful way of life. Let your friends gently (but firmly) restore you.