Universal Truth: Christian, Biblical values are overwhelmingly conservative values. Leftist values are usually in direct contrast to Biblical values. Therefore, a Christian should be a conservative. Liberal Christians are holding and perpetuating values that are inconsistent with Biblical values.
Biblical Viewpoints Are Conservative Viewpoints
For most issues, there is a liberal position versus an opposing conservative or right wing position. In my assessment if one takes his or her Christian faith seriously; and one actually lives out the Biblical values given to us by God; then one would end up overwhelmingly taking conservative positions on most issues. This is because if you take Biblical values and actually apply them to the real world and all the different issues, you result in what's known as conservative values.
Most of what's known as conservative values are virtually all Biblical values. This includes issues that the Bible speak on directly (death penalty, homosexuality, stealing) or indirectly (abortion, capitalism, the size of government).
That's why I'm a conservative and a Republican. If the Bible told me otherwise, I'd be happy to be a liberal Democrat like I used to be when I was an atheist. In fact, my political views are really an extension of my Biblical faith. It's my practical application of God's values. I believe in actually living out my faith ferociously. I don't want to discuss the Bible only on Sundays and at small group. I want to live out God's values every day of the week.
The left-wing values are not Biblical values. That's why most left-leaning people are secular in general. In fact, most people on the left are downright hostile to religion, especially Christianity.
Liberal/Leftist Values Are In Direct Contrast To Biblical, Christian Views
Liberalism As A Competing Religion
As a result, the liberal view and the conservative views are in conflict. There is only one truth. Both positions cannot be right. This means that any honest liberal Christian must choose between Christian/conservative position on an issue and secular/liberal position on an issue. In fact for many people, leftism or liberal political views are dogmas that they are religious about. I know many people like this. For them, the liberal doctrines and beliefs are their religion. This means there is a danger of these liberal, secular, post-modernist views threaten to replace Christianity. That's why most leftists are very hostile to Christianity and Christians. Christianity takes people away from leftist views.
In fact, the Book of Colossians warns against philosophies that are contrary to Christianity and threatens to replace it. I believe that liberalism is one of today's Gnosticism.
Leftist President Obama mocks the Bible and how we cannot base the American society around Biblical principles.
Then Can A Christian Be A Liberal?
Yes, a Christian can be a liberal and take liberal positions on issues. But if you are a Christian, you should take conservative positions on issues since conservative values are the Biblical values.
You don't lose your salvation because you hold liberal views or vote Democrat. Such an idea is ridiculous. However, I would say to a liberal Christian that you are holding views that are contrary to your faith. It's a like a Christian who believes and accepts Jesus as their Savior but still acts inconsistent with the Biblical faith. Examples includes Christians who steal, lie, has pre-marital sex, swears, makes fun of Christians when hanging out with his secular friends, and takes God's name in vein. None of these actions will make you lose your salvation by itself, but that person is dishonoring to God and the values He instructs us to follow.