If you have followed the news, you may know that today is the 2nd anniversary of the imprisonment in Iran of Pastor Saeed Abedini. The First Baptist Church a mile from where I live is holding a prayer vigil for him tonight. Would attending the service be wrong in the eyes of the Catholic Church?
Since you are offering your prayers with your fellow Christians, in my opinion, it would be a good thing. Afterward, it might be good to approach your pastor to see if your parish could organize a Holy Hour or Mass for the victims of ISIS or something similar.
All Christians should pray for and end to the violence.
It’s not like your are participating in their church services, no?
You’re praying. God bless you.