I'll be blunt and honest here, ecumenism is NOT an option for Christians.
Recently I found out in the Metro newspaper that there are Catholics and Anglicans who are teaming up with each other to combat human trafficking and are attempting to stop this abominable practice. While it is fine and dandy to speak out evil and injustice, it is abominable for any Christian to team up with Roman Catholics.
As one who is an Anglican, though probably not forever, I am appalled by this.
This isn't new as High Anglican churches have much in common with Roman Catholicism, minus the Pope.
Those who seek communion with Catholics in fellowship such as William Lane Craig, the late Chuck Colson, Rick Warren and the Archbishop of Canterbury, are disobeying God's word, as the scripture tells us not to seek communion or fellowship with heretics.
Anti-Trinitarians such as Modalists like T.D Jakes or Itzhak Shapira or Roger Perkins or individuals such as Greg Stafford and Anthony Buzzard and many others should not be fellow shipped with, Eastern Orthodox AND Roman Catholics included, despite their acknowledgement of the Biblical Witness of the Trinity.
Keith Thompson of Reformed Apologetics Ministries, along with interviews with Richard Bennett and Robert Zins, have exposed Roman Catholicism as the fraudulent church it is, namely it's mariolatry, idolatry, works salvation, transubstantiation, necromancy, and it's denial of justification by faith alone in Christ alone, in a documentary which can be found here: https://www.youtube.com/watch?v=eS9zSP2udOA
I would exhort the Anglicans who support Roman Catholicism and are reading this to move away from Rome and seek to evangelise them and bring them to the glorious knee of Jesus to whom every knee should bow, in heaven and on earth and under the earth, and every tongue acknowledge that as Lord, to the glory of God the Father.
Addendum, I Meant to say Christians are not to team up with Catholics, NOT Christians are not to team up with Christians. The error has been corrected.
Addendum 2: This article deals with the comment that has been made by XM Flash below: http://answering-judaism.blogspot.co.uk/2014/07/addendum-to-comments-on-anglicans-and.html