Christian ecumenism is good and biblical

Ecumenism is the tolerance and cooperation of Christian churches and denominations with one another. It is the idea that you don't have to be one specific denomination to be a real Christian.

"Good" = Is in line with the perfect and infallible morality of the Christian God.

"Biblical" = Does not contradict the Bible.

In the gospels, Jesus heals people who aren't Jews, the equivalent of the "church" before the apostles established Christ's church. He even tells the thief on the cross that he will join Jesus in paradise, in other words he will be saved. This thief didn't have to join a specific church, just have faith in Christ.

For Jesus to heal people implies they are also saved, because Jesus would only heal those who had faith.

To be clear this doesn't mean that you shouldn't go to church or join a denomination as a Christian, but it does mean that your salvation doesn't depend on being part of a specific institution.

In every church on earth there are good Christians and bad ones, you cannot judge the quality of someone's faith based solely on what denomination they are in unless they happen to be in a heretical denomination that isn't even truly Christian such as Mormons and Jehovah's witnesses.

They cannot know who is right unless they fight each other.

That simply isn't true. They can have civil debates.

There are also essential issues and less essential ones. Your level of ecumenism correlates to how broad the scope of things is that you see as necessary to be Christian.

Jesus defines Christian as having faith in him, and the Nicene creed (which all Christian denominations follow other than fringe loony toons like the mormons) further defines what the core orthodox/correct teachings are that are necessary to consider yourself a Christian church.

They cant know who is right unless they rip each other's beliefs apart. There is no unity with different opinions. In fact, in struggle to gain followers, there might not even be peace.

There can be unity with different opinions, because there is common ground on the essentials of the faith.

As long as they recognize each other as Christians, there is no incentive to treat each other as enemies.

especially since Jesus said to love your enemies, so a true Christian doesn't even treat their enemies as enemies if they can help it.

Fine.