It is not limited to liberal Christians. It is not even limited to Christians. A member of any religious sect will claim that True Believers(tm) are virtuous and good and kind, for example, and anyone who isn't good and kind is therefore Not A True Believer. Usually the counterexamples belong to other sects, but this circular reasoning / question begging comes in handy when one of their own screws up.

I was "saved" at the age of 5, deeply involved in church into my early 30s, attended a Bible Institute full time for a year, was a church pianist and organist, communications director, teach of release-time classes and Sunday School, heralded by one and all as a mature, dedicated, exemplary Christian. Until I wasn't. So now anyone who didn't happen to know me as a Christian simply says I could never truly have ever been a Christian or I would still be a Christian. Even some who knew me "back when" have said that. The rest? They are confused, and think I must have some kind of misunderstanding that will eventually be cleared up, because no one is able to take a True Christian out of the Saviour's hands. They think I've been hurt or disappointed but will ultimately see it was all part of god's plan. I have family members who still talk like this after 25 years.

Your question is a bit malformed and self defeating!

You've identified a class of Christian, that you call Liberal Christians, and attributed a quality to them that they feel "not all Christians are the same or like that" and said that you hate that attribute. But haven't you just committed exactly the same attribute, that you complain of, when you distinguish between Liberal Christians and just normal "Christians".

In any event, I would have thought that it depends on what these Liberal Christians are referring to when they say "not all Christians are like that". It might help you to substitute the word Christains with another grouping, say Footballers, and then it might not irritate you so much because all Footballers show different traits and all Christians similarly have different traits, different thoughts and different lives. Basically, try not to make them change what they say; instead, try to stop yourself getting irritated by it. After all, it's easier to control your own emotions than the words of a mass grouping such as Christians or Footballers!

Alternatively, smoke dope and take a chill pill (joke).

Nothing. Let them fight it out like all religions do. Not out fight. They are judging others.