That being said, there are a lot of ineffective tactics in the left, because there is a lot of infighting (see the XKCD article on standards, as another commenter suggested), and very loose organization.
(And "literature" is a pretty poor way to try to refute the claim, which is what leftists do "in practice".)
If you want to know what any politician will do in power, the process is to see what they are proposing, and to see what others with the same ideology do in practice in other places. If you want to know what the left would do, I suggest doing this.
As right-biased as the two parties are economically, someone wanting to reduce immigration still has no-one to vote for. Even Trump gave nothing but rhetoric and unpopular, ineffective clampdowns on statistically negligible immigration sources, as any graph of US yearly immigration numbers will show.
I'm going out on a limb I suppose, but that isn't how political parties work. Outing myself as an engineer, if I wanted to increase/minimise something in practice I would start with a survey of the academic literature on times where the thing changed radically. Then I would attempt to replicate those conditions. Then I would assess the outcomes using pre-defined measures of success.
No political party works that way. Both wings of policies work near-exclusively with sounds-good-to-people-who-vote strategies. In particular, speaking cheerfully from the right, I've never seen a leftist "minimise [divides] in practice" strategy that looks like it started from a historic survey of what worked. I expect there are similar complaints about the right. I've never seen a political solution assessed for effectiveness, and most of them aren't effective.