The main reason I am not a liberal is because liberalism leans toward naturalism. This is not to say that one who identifies with liberalism always rejects a supernatural explanation for anything, but the idea of freedom is so fundamental in liberalism that it often means freedom from most external authority, and this almost always includes the authority of tradition and religion, and often the authority of a transcendent (supernatural) God.
If there is a rejection of all things transcendent, the naturalist liberal will have some difficulty finding an ultimate purpose to life.
This is not to say that they find no purpose to life. Life can have lots of purpose and meaning within naturalism: Enjoying family and friends (and our animal companions), sports and recreation, the arts and culture, seeking beauty and working hard to make the world a better place.
Purpose, is not the same as ultimate purpose. Many naturalists will accept that their philosophy does not offer an ultimate purpose or meaning to life.
Having no ultimate purpose does not mean living in profound despair. Some live with a defiant courage in the face of oblivion. Others embrace humanity’s natural desire for meaning as a bit of a cosmic joke and just delight in the irony of it all. Many focus on the process and not how it’s all going to end; the process can be a lot of fun. Making cookies with a friend can be very meaningful without the final reward of eating the finished product. For the honest naturalist, these and other approaches are preferable to believing in a supernatural source of meaning.
The least acceptable philosophically, but probably the most common way of avoiding existential despair is to borrow meaning from our Christian heritage. Like the neighbour who borrows our leaf blower then stores it in his garage so long he thinks its his.
These “liberal” ideals borrowed from Christianity can include:
Attending to the needs of the sick and the poor,
Taking care of the environment,
Being hospitable to people who are different than we are,
Fighting for justice for the oppressed,
And freedom for the enslaved,
Recognizing dignity and of all human beings.
There really is no philosophical foundation for these ideals in naturalism. This critique of liberalism is not just mine, actually, it’s Nietzsche’s–so if you really disagree with what I am saying, you might want to take it up with him.
One might ask, “If these are Christian ideals, why does it seem like so many Christians oppose them?”
I suggest there are a couple of things going on here.
For one thing, it “seems” as if Christians oppose Christian ideals, but in actuality lots of Christians and Christian organizations work very hard in all these areas. These things don’t receive as much attention as the those, who work contrary to these Biblical ideals, especially if they are religious.
But unfortunately it is not just a misconception. Some Christians are obviously working against what I have called Christian ideals. But, just as there are many naturalists do not live lives consistent with a naturalist worldview, there are many Christians who do not live lives consistent with Christian ideals.
In the first instance I would call it common sense, in the second, sin.