Galatians 2:12
"For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision."
Being accepted by the crowd is a desire from childhood. Clothing and hair styles become popular because people have a desire to be accepted by the popular crowd. It doesn't matter the age of an individual because people from all ages will oftentimes do whatever it takes to be accepted by the crowd.
Just because a person is a Christian does not negate that desire. Pastors have changed their church philosophy so they would be accepted by their peers. Running with a crowd gives a pastor or church a false identity making them believe they have relevance, but with that desire comes a great danger to compromise truth in return for being accepted by the crowd.
One of the Apostle Peter's weaknesses was that he was influenced by crowds. As boisterous as he was, he truly desired to be accepted by the populous. Peter's desire led to his fear of man. The verse above says that Peter stopped preaching to the Gentiles because he feared "them which were of the circumcision." Peter knew better, but because he desired to run with the crowd, he feared what they would do if he ate with the Gentiles.
Running with the crowd always produces a fear of man. A fear of man will cause one to do anything to be accepted by the crowd. A fear of man will cause one to compromise what they know is true. A fear of man will cause one to deny the church, the faith and even God. Peter did all of these because he wanted to run with the crowd.
If you are going to avoid running with the crowd, then you are going to have to desire acceptance from none other but God. You are going to have to become comfortable with man not always approving what you do. The crowd doesn't always do right. I've watched pastors and churches run to the next big crowd in Christianity no matter where they stand doctrinally all because they desire to be part of the "in crowd." If you keep your eyes on God, it won't matter to you what the crowd does.
Moreover, you will find with whom you should associate by doing right. When you start doing right, you will look beside you and find other people doing right. They don't become your friends and associations because you sought them out, but they became friends and associations because you were both walking down the same path.
Furthermore, if you look to a crowd to determine what you should do, then you will eventually change who you are. The crowd is going to change. They may currently stand for right, but they will eventually change. You must never let the crowd be the horizon of truth; rather, you must let the Word of God and the faith determine truth. When God's Word is your instrument of truth, then it won't matter what others do, because you are comfortable with being alone.
Many good people have gone astray because they wanted to run with the crowd. Many good people have changed because they wanted to be accepted by others. Instead of running with the crowd, you need to run with God. Running with God always leads to staying true to the faith.