The church is a big deal.
Not any particular church. But THE church. THE church is the method to Gods "madness". It is the medium in which he chose to establish change in the world. When you read through Acts, you're reading the story of Eden 2.0. Image bearers of God (holy Spirit indwelt Christians) begin to be fruitful (plant churches) and multiply (add believers) and thus, subdue the earth (make it honor God). So at the risk of sounding like every pastor ever, the church is hugely important in God's redemptive plan for the world.
But just as important as the church, is your involvement in it. The church is nothing without its people. Interestingly enough, the word we use for church in the New Testament is "Ecclesia". It means a gathering of faithful people and in the first few passes as a translation, people used the word "assembly" or "people." So when you read Matthew 16:18, it was read like, "and I tell you, you are Peter, and on this rock I will build my people, and the gates of hell shall not prevail against it."
So the very word "church" refers to you.
It wasn't until later iterations that some germanic translators started using their word "kirika" which meant "building". We moved from referring to the people into calling it the building. But this changes the concept that Jesus and the Apostles had in mind when they wrote the New Testament.
If God is building a building or a global organization, then it doesn't really matter whose in it or not. As long as SOMEONE is in it, then it's fulfilling the mission. But that goes against the character of God who has shown himself to be a loving and highly relational being.
But if God is building a people. Then He wants you. And me. And every other individual to be part of this thing we call church.
So how does that answer my original question: when is it okay to leave your church?
If the goal is to create a people group, then that means it requires something of us. A building can be left and returned to whenever without much cause or care. But people are way too emotionally invest in each other for that to occur. If you come into someone's life one minute but leave the next, you've lost influence and trust with that person.
So the church is something that requires us to be committed. You may have heard a church called "a church family" and, in a way, that's actually a really good analogy for the metrics I'll give for when I think it's okay to leave your church.
1. They lost sight of the gospel
The big reason to leave a church is they stop preaching the gospel. They might talk about Jesus or the Bible. The pastor might be really smart or highly relational. But if no one is coming to Christ and people aren't hearing that God created them, God commands them to live certain ways, we rebel and sin against him, and Jesus saves us from our just punishment, then it's time to leave that church.
2. You cannot ethically follow that leader
Notice I said ethically. There are lots of leaders that I don't particularly like, but that just means they have a different style than I do. If it has to do with moral failings or maybe even offenses given, it's only after you follow the Matthew 18 style of reconciliation that you can justly and biblically say that you should leave that church.
3. If you are not being allowed to serve
Once you become a Christian, the greatest and fastest way to grow in your love for Christ is by serving his bride. If you are in a place that is constantly saying, "we don't have room for you" or "that doesn't fit here" then it's time to find a new place to serve.
4. If you are sacrificing your families growth by being there
Some churches are tailored to specific people. I hope you find one that is well rounded, has a good kids ministry, youth programs, and adult discipleship. But occasionally, you'll find one with lackluster youth program when you have a struggling teenager. If the pastoral staff is not showing any improvement (including accepting your help to improve it) then you should not stay there just because you like your Bible study. The church your family attends should benefit your FAMILY.
That's my list. It's short but I want you to notice that I didn't include worship style, bad preaching, or lack of groups. All of those are fixable problems, but they are only fixable if you stay in the church, give feedback, and offer to help. Americans tend to be on the lazy side of the spectrum in that we only like to see solutions but we never want to be the one that works at the problem. That is incongruent with the Jesus of the Bible and the Church of the New Testament. So get in there, roll up your sleeves, and BE the church you want to see in the world.