The best way I have learned to perceive it is that those of the "left" are best akin to a set of islands, loosely connected in that they are close enough to each other in range. Just like how different islands have different cultures, ecosystems, terrains, you find that the different groups of people of the "left" are that way, with their sole united fact being that they aren't the "other side"; however, when you ask where the line of the other side is, they all mark the line at a different point, some even going to far as to say those on the other lines are part of that "other side."
In my own experiences, I have seen this in discussions of equity, especially racial equity as a person who is mixed race, equity and rights for those who are LGBTQIA+ as a person who is part of the acronym, and the care for the environment.
I sadly have no true solution for this issue. People almost strive on the idea of disunity, being the sole group that has their perception of the proper answer, the single truth, and developing inane criteria to compare others to that aren't part of their same group, solely to justify hating them.