After I left college I spent the next few years in groups that were, what might be called, non-denominationals. I was introduced to a deeper understanding and experience of the Holy Spirit in those groups. We were known at that time as Jesus freaks. But we had little structure and no fences at all. Of course, we would say that the Bible was our fence and whereas the Bible is a good fence the problem was that people could get things from the Bible that were beyond the fences of other denominational groups or even most denominational groups. This opened the door to strange and fantastical teachings that led people down one path and then another, being tossed on the waves of whoever was the latest "charismatic" leader.
That's why I have come to like fences and thus "denominations." At least with denominations you know where the fences are. The well known experiment of taking fences down from school yards led most of the students to staying close to the building for security. But there would be some who would venture beyond the school yard and sometimes put themselves in danger. When the fences were put back up the students played all over the school yard right up to the fences without fear. I have been in a conservative denomination for the past 42 years. I confess that I have played right up to the fences but I enjoy the security of staying in the school yard.
Fences are what might be called confessions or creeds. They say to the members of that tribe that you can go so far and no further. There are denominations that differ from mine that also have fences of their own. On many points their fences are the same as mine but in some other points they differ. But at least I know where we differ and we can engage in civil and constructive conversations. In fact I might even be able to learn from them as long as I can do so within my own fences. While at seminary we arranged dialogues with another seminary nearby from a different denomination. Both of our denominations had strong fences that were built upon the Bible and so we could listen to professors from both seminaries without fear of being contaminated. We knew where we all stood. In that setting we could grow from the dialogues.
It is true that some denominations have moved their fences. I, for one, do not like the moving of fences. When a fence is moved it is encroaching on the property of another. Some have moved their fences so far that they are now encroaching on the property of pagans. Now, I do not hate pagans but when a denomination has to extend their fences to the point that pagans are now in their fold they cease to be a distinct group. They are no longer just in the world; they are of the world. Yet even these denominations have fences, albeit wider fences than I would be happy with. But at least I know where they stand and I can choose whether or not to associate with them.
Non-denominations are in another category all together. They have no fences. Within their fold they have people that might better fit in a variety of other folds. They think that this is the charitable way to be but like children in the school yard with no fences it leaves their flock far more vulnerable to wolves in sheep's clothing. Fences not only keep the sheep in but also keep the wolves out. Some of those wolves have come in with the idea of exchanging faithfulness to truth for turning the Gospel into a scheme to make money. Others have come in teaching that the Old Testament God is not the same as the New Testament God and teach a new kind of antinomianism. That's just a fancy word for saying that the Law is no longer relevant for the Christian. The New Testament would call them Nicolaitans, compared with Balaam, who taught Balaak that the best way to bring down the people of Israel was to tempt them to forsake their commandments.
Non-denominationalism, with its aversion to fences, i.e. confessions and creeds, is only held together by the charisma of its leader. If he is a good and Biblical leader, having fences of his own, the church may do well. But he will not last forever and if there is a new leader who comes without the same solid footing, the church will easily succumb to the latest heresy coming down the pike.
In short, that is why I prefer denominational churches, especially my own, to non-denominational churches.