I distinguish between Liberals and Leftists (as well as Conservatives and Rightists).
You can be for example, a Patriot, but not a Nationalist. Patriots believe their country has values worth upholding but distinguish between the country, "patria" and the current political regime that runs it, whereas Nationalists tend to confuse government with nation.
Liberals typically have some nice, Libertarian like ideas of how to improve society, but they agree with the essential tenant that human beings are not angels. Human beings can be perfected - according to them, but it will take time and good education, environment, etc. as well as INDIVIDUAL effort.
Leftists however do seem to think that human beings are either angels who will obey the law if only some law is passed or some court says so, or demons to be annihilated. They ASSUME that people will be made PERFECT despite themselves by a SYSTEM of law and government. So if people go nuts and rape, loot, and murder 7 year old girls....the Leftist sees the failure of "society" or "government" not a moral failure of an individual person.
Liberals tend to want more and more rights - to be "left alone". But they become Leftists when they try to find an origin of all these rights in the state as opposed to something preceeding the state, human nature.
I can deal with "liberals". Especially the JFK liberals (which are almost the same thing issue by issue as Reagan Conservatives). But liberals who think rights are created out of thin air by courts or that absolute minorities can re-define words and institutions at whim, often start out with a veneer of intellectual rigor but become Leftists by logical regression.
If your premise is wrong - whether we're talking rights or economics or history, then your conclusions will be wrong. Conservatives or Liberals who maintain an "open mind" can acknowledge when they've made a mistake. Leftists (or "Rightists") are ideologues and hence can't admit to mistakes.