Why can’t someone who believes it is wrong to worship using a musical instrument sing when there is a musical instrument playing? The person singing is not playing the musical instrument.The person singing is singing.
“It would be a bad example. It would look like you approve of the musical instrument. The music doesn’t stop halfway across the room. Everyone in the congregation is worshiping with the musical instrument.” What if a man prayed incorrectly during the worship service? Were you a bad example if you worshiped with that congregation? What if a man worshipped alongside a woman with a head covering on when he did not believe in women wearing a head covering in worship? Or worse, what if a man worshiped alongside a woman who was not wearing a head covering, when he believed she should be wearing a head covering (as about 5% of members in the non-institutional churches of Christ believe–I Corinthians 11)? What if you worshiped alongside a teenager wearing a mini skirt to church? Wouldn’t it look like you approved of her mini skirt? Wouldn’t you be a bad example? What if you were on vacation and worshiped at a Church of Christ that had some odd beliefs, beliefs that your church back home did not have? (This has happened to almost everyone at least once in the Churches of Christ.) Were you being a bad example by worshiping with them?
The apostle Paul said in Romans 14 that one person esteems one day above another (Sunday), and one person views all days the same. Obviously one person is wrong in this case, they can’t both be right. Yet the apostle Paul said not to worry about it. Let the two worship in peace. So we could have someone worship by singing while someone else worships by playing a musical instrument. One of them could be wrong (as in Romans 14) and we could accept one another. In fact we are commanded to accept one another.