Ephesians 5:11 And have no fellowship with the unfruitful works of darkness, but rather reprove them.
Jewish synagogues include no paganism. I still don't attend them as they have been set aside by God "until the time of the Gentiles" comes in.
I think I understand what you wrote. It seems to me it is a matter of conscience for you, given that interpretation, only to fellowship with like minded people. It seems to me you consider Catholic assemblies, where we publicly confess Jesus LORD and Christ, crucified for our sinsm , risen from the dead, ascended to heaven, seated at the right hand of the Father, until he comes again to judge the living and the dead, "unfruitful works of darkness." It seems clear to me why this kind of Protestantism/Evangelicalism/Otherism would produce vehement denunciations of both Catholic and Jewish doctrines and customs. I would think it very difficult to have any real friendship or dialogue with either Catholics or Jews given that premise (all that is available is street fighting, oops street evangelism). Catholics, on the other hand, regard Jews as elder brethren, and while they may argue can make long enduring friendships of love.