One problem with Christianity is that it is mixed up with Judaism and the very different values, beliefs and behaviour of the people of Israel in the Old Testament. With its quite shocking track record down the centuries, even to the present day, Christianity I think, should really be confined to the life and teachings of Christ in the Gospels. His teachings should not have been mixed up with scores of other teachers, prophets and kings outside of four New Testament books in the Bible of 66 books. Christians have to be syncretists and to take on board so much that it is different from Christ's values and practices. You then have to be into defending the indefensible or, cherry picking the more ethical teaching and, even explaining what should, simply, be repented of.
Problem two is what my youngest brother in law mentioned to me at Christmas. He had read the mighty tome called 'A History of Christianity - over the last three thousand years'. One conclusion he came to was that Christianity's history has been noted by a love for truth rather than a desire for unity. I agree. I have found division, conflict and war within Christianity and out to others since the conversion of Emperor Constantine. Nothing changed with the rise of secularism over the last 100 years. War to defend our vital strategic interests around the globe is as common among the secularists as the church-goers.
Down the centuries, Christians have slugged it out between the different denominations and churches of Christendom. Now, against the Muslims and the Taliban in Afghanistan and the border with Pakistan whose killings we justify 'cos they are the terrorists and we are the angels of light, truth and justice; the angels of goodness bringing democracy and Western values to those who don't know better! All the Christian churches - and everyone else - are fully involved apart from the Quakers, whom the evangelical Christians sadly shake their heads at as not being Christians, at all.