I thought it means "dogwhistling", except for the political left instead of the right?
On the right, it might be: murder is bad, therefore I oppose abortion.
On the left: gay marriage is good, and opposition to it is homophobia, therefore Brandon Eich should be fired.
When the link between X and Y is too specious, it implies the speaker's primary goal is to show virtue by opposing X, rather than any real concern they have about Y.