In the realm of the political, I think a set of basic questions will work in almost all cases:
What is it (how is it defined)?
Is it wrong?
Why?
Is it always wrong? If not, why not?
Any leftist you take through this exercise will quickly contradict themselves. Take racism. They will tell you it is wrong, that it is group prejudice/hate against another group, and that it is wrong because we are supposed to be nice to each other.
But is it wrong when, say, blacks hate whites? What about when blacks hate hispanics? What about when British Pakistanis hate Jews?
This will give them trouble. You then ask again: if this is not a universal principle, what is it? If we are supposed to be nice to each other and people are not being nice, then that is bad, right?
The reason this gives them trouble is that they have only apparently embraced universal principles, notions of universal human rights. Slavery in the South was wrong, but slavery in the Soviet Union was freedom (how is slavery defined again, and why is it wrong? )
Leftism is a cult of conformity. They are told which forms of slavery are wrong, and which are acceptable. Their reactions are dictated by the culture within which they live, which is post-Rationalist, and atavistic. They live only figuratively in caves now, but may yet engineer it as literal fact for all of us, at great cost in human life and unimaginable misery.
Edit: I will add that I myself have “decontructed” “universal moral principles” of an historical sort. I do not say slavery is always wrong or right. I have renounced the right to tell people what they should do. Certainly, where my interests or those of those I love are affected, I retain the right to make decisions.
I have argued that Goodness is the eventual result of rejecting self pity, cultivating perseverance, and learning something new every day forever. I have defined Goodness, in turn, as being capable of enjoying with them the happiness of others, and being able to be happy on your own. You benefit people, and benefit from them, but don’t need them (neediness clouds judgment, which is to say perceptual skill, and the whole thing relies on perception.)
I have further argued that all proper moral decisions are local, imperfect, and necessary.
Leftism, though, IS a moral narrative. The entire thing rests on seemingly universal moral claims, but claims which are inherently, internally, contradictory. It is an extraordinarily judgement creed resting on an intellectual base of sand.
I both critique political radicals, and offer an alternative to a return to orthodox religion. That is my aim.