Then God is a God of confusion, since it is self-evident that no two people agree on *everything* in Scripture, contrary to what you say the Spirit should ensure. Since such Spirit-led agreement simply does not exist, your position is without foundation.
As for the church being composed of all believers, again, you have God's intent all wrong. Jesus prayed HARD for unity in His future Church in John 17 because it is so vitally important. the tenous, vague sort of umbrella church you propose has no teeth, and that is preceisely why Christianity tends to be so ineffective against the encroachments of unbelievers in the modern world.
"Church" appears 84 times in the English NT. It is our translation of the Greek word ekklesia. To the Greeks it meant "any public assembly of people." It became an appropriate description of the Christian community, for they regularly met together for the purposes of worship, teaching, fellowship and celebration.
Our English word is taken from the Greek adjective kyrikon. It means "belonging to the Lord." Again, this term is an accurate description, because the Church is composed of those who "belong to the Lord." That is the one and only Biblical criteria for membership.
It is clear that the early church saw itself as a community rather than an institution. In the Book of Acts, the believers refer to the church as "the brethren", "the disciples", "followers of the way", or "saints." It was not until later that the term "ekklesia" began to be used to describe the community of believers.