Why I'm not particularly Ecumenical

Many churches, not least Congregational churches, enjoy boasting about their ecumenism. The Ecumenical Movement attempts to reunite the various Christian denominations. Historical rivalry and suspicion are never wholesome, and inter-church cooperation is noble. It's taken for granted now that as a pastor you're ecumenically minded. But I'm not. Why?

1) Christ's true church has never been divided; there are no genuine divisions to heal. A born-again baptist, Anglican, or pentecostal is already my brother or sister. I don't need formal union or joint meetings to prove or demonstrate this. The unity is already there. 
2) Much ecumenism is a response to decline. Shrinking congregations and declining denominations have forced some churches to cut their losses. I say that churches should get back to the Bible and preach the gospel. This will cause the churches to grow and stay the decline. Ecumenism seems an attempt at merely managing this decline.
3) We already work together and do no need formal ecumenical unions to achieve this. At Martin Top, we have Methodist, Reformed, Anglican and Pentecostal preachers. If they preach the truth, we'll hear them, regardless of their churchmanship. I'd sooner listen to an evangelical charismatic than a liberal Congregationalist. 
4) Ecumenism overlooks and ignores theological error. Some beliefs, such as the millennium of Christ's return, baptism or predestination are important, but we have to agree to differ. I'm premillennial, but I acknowledge that others sincerely, and intelligently, hold to other views. But some doctrines are simply too fundamental to dispense with. When David Jenkins, former Bishop of Durham, denied Christ's resurrection, he merely proved that Christ and Belial have nothing in common. These people went out from us, but were not of us. With such as he, and other vipers in the Lord's vineyard, we cannot unite.
5) Ecumenism nullifies and undermines the Reformation. Protestants broke from Rome for genuinely worthwhile reasons. I'd make myself popular by saying Catholicism is just another church, but I can't. Although it gets much right- the trinity, the deity of Christ, the sanctity of life and the marriage bed, it gets many fundamentals wrong. For example, the 39 Articles of the Church of England rightly state:
"Wherefore that we are justified by faith only, is a most wholesome doctrine, and very full of comfort".
Contrast this to the statement made by the Council of Trent a few years later, fully endorsed by the Roman Church of today:
"If anyone states that by faith alone the impious is justified...and that it is not in any way necessary that he be prepared and disposed by the movement of his own will, let him be anathema".
If being ecumenical means sweeping Justification by Faith into the dustbin, then the summer is over, and we are not saved. Some doctrines are too precious to compromise. I was in Naples this week; I took the picture below in the main cathedral. It was stuck beneath a statue. This is why I'm not ecumenical.