Uh, it is contested because you're basically attributing a lot of things to liberalism that really didn't have anything to do with liberalism.
In fact, did you know that Thomas Jefferson, a raging liberal of his day, was a slave owner?
Did you know it was the Republican Party that waged the war of aggression against the South?
Working conditions have nothing to do with liberal vs. conservative, left vs. right, nothing to do with it. It DOES have a lot to do with PEOPLE recognizing a **** situation in their lives, seeing that there is room for positive change, and then doing things to move towards it. That is completely unconnected with politics, but political factions were able to sense the change in the wind for those issues and grabbed on to it to gain votes. If you make the mistake that a political ideology is always correct, you're going to end up being led down the path of believing things that aren't true. You need to see the truth unconnected with political factions, otherwise you're going to end up being manipulated at some later point.