It is true that some preach Christ out of envy and rivalry, but others out of goodwill.  The latter do so in love, knowing that I am put here for the defense of the gospel.  The former preach Christ out of selfish ambition, not sincerely, supposing that they can stir up trouble for me while I am in chains.  BUT WHAT DOES IT MATTER? The important thing is that in every way, whether from false motives or true, Christ is preached. And because of this I rejoice. 
Philippians 1:15-18

Now John’s disciples and the Pharisees were fasting. Some people came and asked Jesus, “How is it that John’s disciples and the disciples of the Pharisees are fasting, but yours are not?”
Mark 2:18

They came to John and said to him, “Rabbi, that man who was with you on the other side of the Jordan—the one you testified about—well, he is baptizing, and everyone is going to him.”
John 3:26

When the disciples James and John saw this, they asked, “Lord, do you want us to call fire down from heaven to destroy them ?”
Luke 9:54

My brothers, some from Chloe’s household have informed me that there are quarrels among you. What I mean is this: One of you says, “I follow Paul”; another, “I follow Apollos”; another, “I follow Cephas ”; still another, “I follow Christ.”  Is Christ divided?
1 Corinthians 1:11-13

When I came to you, brothers, I did not come with eloquence or superior wisdom as I proclaimed to you the testimony about God.  For I resolved to know nothing while I was with you except Jesus Christ and him crucified.
1 Corinthians 2:1-2

People notice when we bicker among ourselves.  I have heard Christians ripping apart other Christians over whether they believe in issues such as the gift of tongues, women in ministry, end times scenarios, and other similar issues on which wonderful godly people have different viewpoints.  And guess who watches this?  The younger Christians in our churches, and then those on the outside of our churches wind up hearing about these things.
Dan Kimball, They Like Jesus But Not the Church

With the tongue we praise our Lord and Father, and with it we curse men, who have been made in God’s likeness.  Out of the same mouth come praise and cursing. My brothers, this should not be.
James 3:9-10