The atheists aren't alone in mocking. If you've been on this site for any length of time you know there are many Christians who mock and insult other Christians. In fact, IMO we are the biggest bunch of bickering, back-stabbing communicators I can think of.
In my opinion you have hit on something here. Having made a hobby of debating on liberal and atheists forums on the net, it is with a very illogical arrogance with which this group mocks Christians, especially do they mock Christians who believe in a born again experience. Two mental frame of references are identifiable in this type of exchange.
First, there is the mind set that the liberal and atheist believe they possess a superior understanding of reality than the Christian has. This group sees Christianity as somewhat a superstitious belief. Even liberal so called Christians will often say that you can not really prove there is a God and point to the assumption that Christianity is a matter of faith, thus, admitting Christianity is not based on proven facts.
This type of reasoning is terribly wrong but too often Christians do not know why this type of reasoning is terribly wrong. Because not knowing how to show this reasoning is terribly wrong, the Christian becomes a subject of ridicule.
The truth of the matter: it is fun to but in on a debate between the Christian that is being mocked by an atheist. The reason is that the atheist is so foolish in this debate because every premise he uses depends on an assumption of a premise that requires a belief in God. Faith is not a nothing, faith is a substance just as real as any piece of matter is a substance. The simplest of people know there is two parts of reality: (1) ontological and (2) cosmological. This is a theme throughout the Bible and common among philosophers for metaphysics requires both mental recognition and solidarity of things to equal reality. Faith is evidence of things not seen. A rock or a noise is meaningless without recognition by a knowing being that these thing exist. In this way even physical things and knowing is necessary for reality to be.
This is the reasoning necessary for the self evident rights, truths, and liberties cited in the Constitution of the USA. This is the premise of the American belief that our rights and freedom come from God and is the reason Americans believe we are a Christian nation. God is the greatest self evident truth in the universe.
To ask a liberal or atheist to prove their is not a God is a very frustrating to an atheist or to a doubter. If you ever bring an atheist to this point of discussion, he will ban you from this part of his web site. He will claim the burden of prof is all yours. He does not think the rules of logic applies to him and his ways of thinking does not need an ontology (theory of being) or a reason to say there is no God. How foolish is this type of thinking?
The second fault an atheist has is that he does not understand that he must believe in the preexistence of God as an ontological being just to be a reasoning being himself.Modern day thinking of liberals and atheist is that there is no ontology that was not created by cosmology. This type of thinking is called phenomenological philosophy and is the main type of reasoning used in liberalism on most college and university campuses in America and Europe. Note that most liberals in this world are atheist. Demographically there are very few liberals that are Christians, but there are some whose search for truth has led them to Christ. So, we are not saying a liberal is not always an atheist.