I've never heard anyone say it's a sin. Although I did hear brother N.A. Urshan say the thing in a message about homosexuals wearing beards cut a certain way to identify them as homosexuals, like wearing a ear ring in a certain ear. He didn't say it was a sin; but he said just like everyone else I've ever heard say about it, that we shouldn't look like the world.
I can see that because people in the world see on the outside before they notice what you have inwardly. The outwardly will make them analyze you and allow them to see you are different inwardly. That's the only way I've ever heard it preached. Though I have heard when you start to rebel against your pastor the first thing someone will do will start with their hair or facial hair most times. So I can say beware,
1 Samuel 15:23 is something we should all stay aware of!!
2 Corinthians 13:5 "Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?" And nobody became a reprobate all in one night, it starts one decision and compromise at a time. I encourage you to take a stand on that serpents head and don't let off.
Here comes the attack, but as Pilate said in
John 19:22 "What I have written I have written."