Now there are many ways to answer this matter, but I'll just break it down into 4 logical steps and let you take it from there. Here we go.
1) The first and most basic tenet of the Christian faith is "Jesus is Lord".
2) The New Testament is chock full of "one-another" commands which are impossible to obey apart from commitment to a local church.
3) By remaining uninvolved in a church, you declare that you have absolutely no intent of obeying these numerous commands.
4) Which is, shall we say, incompatible with the statement that Jesus is Lord.
And that's all you need to know my thoughts on this matter.