As I understand more about politics and science, I'm realizing that dishonest or ideologically blind people can make inaccurate statements using accurate data and supporting evidence.
That makes it all the more important to be dedicated to discovering and finding the truth no matter the consequences (liberal). Unfortunately, many who call themselves liberal are actually very illiberal in both style and substance. They advance a left-wing agenda just as forcefully as the right-wing without a commitment to intellectual honesty.
One example that interests me of why it is desirable to be a liberal comes from the New Republic where they examine Alan Simpson's claim about the fiscal "problem" of people living longer on Social Security than in past decades. The trouble with his actual figures were that he was comparing total life expectancy which includes people who died from childhood diseases in the 1940's, to current data which in general doesn't include that because we have cured many of those illnesses. So that "shorter life span" he's referring to is exaggerated because it includes people who died well before they either contributed to or collected from the Social Security system.
This is not to say there's no problem but the facts matter when you make public statements.