A lot of people are using this very effective tactic -- demand that the Leftist state their premise. Take them back to their foundations and ask them to build their argument from first principles. They just can't. They don't know (or, more likely: don't want to admit) why they hold their political beliefs.
It's all about them feeling good about themselves. From a rational standpoint, they have absolutely nothing.
BINGO!
That is THE way to completely dismantle any leftist argument.
1) Demand they define terms. (fairness, justice, equality)
2) Demand they give a basis for their beliefs and assertions.
You usually don’t get past these two.
Yes, it IS all about them feeling good about themselves (Sowell: Intellectuals and Society) and they usually haven’t thought about WHY they believe what they assert they believe.