The problem is one of scriptural authority for the teachings and practices that are done in the name of Christ. Scriptural authority is found in direct commands from Christ or the Apostles, approved examples by Christ and the Apostles and Disciples, and NECESSARY inferences. It is this last category that causes a great many problems. Another problem is the inability of people to recognize the difference between SPECIFIC authority, and GENERIC authority. Some people have the notion that if the scripture does not forbid something, it is permissible to do that thing, while others believe that one can only do what has been directly stated as acceptable by the scripture.
Scripture teaches us that the Christians in the time of the Apostles gathered together in church on every first day of the week to worship. That is approved example, in addition to the command to take the Lord's Supper on the first day of the week. The Christians were also commanded to lay by in store on the first day of the week. How then can anyone justify a practice of NOT attending worship services on the first day of every week, and claim to be following the teachings of God?
The scripture tells Christians to study the scripture, to pray, and to sing and make melody in their hearts. How does that become authorization for pianos or organs or even rock band performances? How does the command to sing translate into having a choir that most people listen to, instead of participating in the singing themselves. When did entertainment become the primary purpose of the worship service, instead of obeying God and glorifying God by the obedience?
Christians are each considered to be a priest, and the high priest is Jesus Christ. There is no mention in the new testament of a separate priestly class that people must seek out to intercede for them, or to hear their confessions. Christians are told to confess their sins to one another, to the church, not to a special confessor that will hide their shame and make it easier to continue living in sinful practices. The scripture does not authorize selling indulgences, or buying one's relative out of purgatory. Christians are taught that there is only one spiritual father, and only God is to be called Reverend.
There are many practices, taught by many denominations, that are in clear violation of what is taught in the scripture. Why are those practices accepted by the members of those denominations? The members are ignorant of what the scripture teaches, because they have been taught that the scripture is too difficult for the common person to understand, and they need a specialist to explain to to them. Thus the doctrines of men and the denomination of the church, instead of the unity in obedience to God.