In a perfect world, Christianity (or even the more generic faith in God) would be uniting.
But, in our modern, imperfect world, too much of Christianity identifies themselves not so much as followers of the Lamb, but followers of the GOP agenda. Beginning in the 1970's with people like Jerry Falwelll and Pat Robertson, a deliberate movement was started to co-opt Christ into the Republican Party and adopt the party's platform as defacto evidence of true Christian "faith."
That this doctrine of devils has succeeded is admirably demonstrated by the OP's assertion that liberals (a political definition) can't possibly be Christian's. Very often, we even hear non-conforming (i.e. non-conservative) Christian's identified as enemies of Christ!
The Jesus Christ of the Evangelical movement is anything but uniting because the message supposedly coming from Him is intolerant, unforgiving, bigoted and selfish.
That's not the Jesus Christ of the Bible.
It's not the Jesus Christ of most of the Christians in the world either despite the fact that the anti-religion groups scour the Earth for something, anything, however rarely anecdotal or however removed from the current culture, that they can use to demonize Christianity.
The evidence remains that it is almost--not quite all but almost--always the Christians you find working with the homeless in the cities, staffing the soup kitchens, supervising the shelters, and organizing and manning the thrift shops and food pantries and retraining centers. It is some of the most legalistic, narrow minded, fundamentalist Christians that routinely risk their very lives to get relief supplies into devastated but dangerous areas, who devote years to work in the leper colonies, in the poorest neighborhoods of Calcutta, Bangladesh, and Africa among people who never heard of Jesus Christ, much less are Christian. They define tolerance as loving God's people whoever and wherever they are.
It is mostly Christians who pushed for hellfire towns to be tamed, for schools and churches to be built, and for law instead of vengeance to be the policy. It is mostly Christians who pushed for an end to slavery, for women's suffrage, for civil rights.
It is mostly Christians who defend marriage, not for religious reasons but for the benefit of the children and society, who give up their vacations year after year to spend two to four weeks among the poor in Peru and southeast Asia and other remote places to fit refurbished wheel chairs, walkers, braces, and other liberating equipment to people who would never have had access to these things or would never have been able to afford them. It is mostly Christians, many from America, who staff orphanages in some of the poorest and most dangerous neighborhoods in Mexico and establish and maintain ranches for orphaned or troubled children here in America.
Hundreds of millions of Christians everywhere are going about their business, paying their taxes, obeying the laws, being good citizens and being a credit to their communities, while sharing their time, talent, and ability in volunteer work to help others and/or giving significantly from their material holdings to help support all those other miinistries all over the world.
When you can point to any organizations of Atheists or any other groups who do as much for so many, without publicity, without recognition, without much if anything in the way of financial reward, and often at the risk of their own health, safety, and well being, then you can accuse Christians in general of not being Christian.
Now you can focus on these who are the rule. Or you can look for the anecdotal evidence that are the exceptions.