Liberal Christians believe that some parts of the Bible are symbolic in some way or other and not everything there is literally true. Liberal Christians have less difficulty explaining contradictions in the Bible and bad moral teachings there. They simply say that those parts aren’t literally true. They tend to accept the nice parts of the Bible. Liberal Christians tend to follow similar policies to other political liberals. Many liberal Christians are nice people but they tend to be a bit credulous.
Some Liberal Christians may even accept that parts of the Bible are legends. Liberal Christians are likely to be Old Earth Creationists and/or Theistic evolutionists and are generally more sensible than Fundamentalists.
Even Liberal Christians are irrational as there is no reason to believe in very much of Christianity, other than the fact that you can.  Liberal Christianity is also in some ways harmful because it too supports invalid claims. One of the most basic beliefs of many sections of Christianity is that all non-Christians will be tormented in Hell. Christian Universalists do not believe that anyone will be tormented eternally in Hell, while many other liberal Christians prefer not to think about that question (a prime example of this is Joel Osteen).
Helping fundamentalists indirectly
Moderate theists and moderate Christians indirectly help Christian fundamentalists to exist. When children have been indoctrinated to believe in any type of Christianity they are vulnerable to fundamentalism. Many children are brought up in moderate Christian churches where Hell is not discussed and superficially things look acceptable. Inevitably when these children are old enough to go out on their own they will come across Hellfire evangelists that are found at street corners in all English speaking countries and many other countries as well. These street corner evangelists will tell the children that Hell exists, they will show the children passages in the Bible referring to hell and a lifetime of care to teach only the pleasant side of Christianity can be undone in five to ten minutes. Alternatively the children may go into a fundamentalist church to worship and the liberal Christianity they‘ve been taught will be undermined there more gradually but more surely.
Preventing scientific debate
It is claimed that moderate theists prevent proper scientific debate about religion in media that mainstream people access. Christian fundamentalists certainly do that as well where they can. Christians of all types fear that their beliefs will fail Scientific tests and lose in scientific debates, so they do what they can to prevent such discussion. Non overlapping magisteria are an example of where even liberal Christians try to limit Science.
This wiki and Liberal Christianity
This wiki concentrates its attacks against Christian fundamentalism because fundamentalists clearly do harm. Moderate Christianity has fewer harmful effects.