Liberal Christianity could be defined in theological terms as a type of Christianity which has gone far towards abandoning the historical and literal aspects of Christianity - but its essence is really that Liberal Christians have - over time, through more than a century, and with some time lag - fitted Christianity into the prevailing secular morality.
This means that Liberal Christians are nowadays on the political Left (a term which also includes all mainstream 'Right wing', conservatives, republicans and libertarians) - in particular in terms of their focus on the key Leftist moral issues of the day: feminism, antiracism, diversity, climate change, third world poverty - and the sexual revolution in general. Liberal Christians embrace these causes; and usually put them at or near the focus of their self-identified Christian life.
And this is precisely why Liberal Christians are, as a strong generalization, useless. By useless, I mean that being a Liberal Christin makes almost no perceptible difference to its adherents - who are assimilated to mainstream modern life in all significant respects; and by useless I mean that Liberal Christian Churches do no good in combating - or even in fighting - the besetting sins of modern times.
Indeed, Liberal Christian churches have no distinctive role at all. They do not address the besetting sin, so they are useless to Christians where it matters most; and they do assimilate to mainstream modern morality, which renders them superfluous to non-Christians. This is a major reason why all Liberal Christian groups in all denominations are shrinking - both in numbers of adherents and in the devoutness of adherents.
The reason is that the besetting sins of modernity - those sins to which we are most prone, and which most harm us - are all Leftist sins: including the anti-spiritual, anti-religious positivistic materialism that has utterly taken over all public discourse (including the public discourses and communications of mainstream Liberal Churches, which nowadays barely mention religions matters).
How do we know the besetting sins? A society's besetting sins are those sins that are actually approved and encouraged in high status, official public discourse.
We as individuals and as as society are trapped by our besetting sins - many of which are transcendental inversions - Good renamed as evil; the destruction of Good being called good.
Only by first addressing our societies besetting sins can we even begin the process of spiritual progression; and conversely those who are part of the modern moral mainstream (which is Leftist) cannot even begin to do the one thing needful.
Because the one thing needful is to reject the besetting sins of our era - and Liberal Christians do not even want to do that; since they have chosen to regard the besetting sins of modernity as their major priority.
Note: There are, of course, significant problems, limitations and deficiencies with many non-Liberal Christian churches and denominations - in particular relating to their implicit acceptance of the unspiritual, alienating and mechanistic consciousness of modernity. But Liberal Christians and their churches are of no use in changing Christianity in the necessary direction, nor in assisting genuine spiritual development, because they have in practice allied with the primary forces (the international ruling elites, the media, the bureaucracy, officialdom, corporations...) that are excluding and suppressing the reality of the spiritual.