It seems here that we are dealing mostly with secondary issues. When it comes to primary issues(doctrine) that christians should believe ie Triune God, Death of Jesus on the Cross, His resurrection, sin, hell, mans sinful nature, etc should be held with a closed fist and are issues that division will occur when someone or some institution tries to change or oppose these truths. The things that are held with a open hand would be infant baptism/dedications, free will/predestination, preterist/dispensationalist/pre trib/ etc, types of music, speaking in tongues, are all examples of things we can debate on and argue over but should never divide over.
A couple of examples here in Canada of churches no longer being churches of God are the United Church and the Anglican Church. For there twisting of scripture on the true definition of sin in regards to homosexuality. This is a prime example of when someone should leave the church when it no longer holds fast to what is good.