Agreed on your general point—but the OP asked the question so it is reasonable to answer it with details.
The way I deal with leftist relatives—since I agree with your view—is I do not offer details.
I let them talk and find specific points they made which contradict other points—and make sure they know there is a contradiction.
Examples:
—They love unions and love illegal immigration which undercuts wages.
—They love Muslims and love “women power” even though Muslims treat women as second class citizens.
—They think “race does not matter” and then favor programs which benefit specific racial groups.
etc etc etc.