If I had to say what the single biggest problem is with the world, I'd say "group identity".
The definition of group identity is, "You're not fundamentally an individual but part of a group". This is the thinking at the heart of all of the following evils:
Communism: The people exist not as individuals but as parts of a nation, so we have to force them to pool everything and individuals shouldn't be allowed to keep the fruits of their labor.
Democracy: "We The People" made this law; therefore everyone who's part of "We The People" should be violently forced to comply even if they voted against it and never consented to this system.
Leftist identity politics: "White people are the dominant group and racial minorities are victims! Therefore every member of a minority race is a victim and every white person is part of the kyriarchy!"
Species conservatism: "It's the last of its kind! It deserves to be specially protected even though it's just a single animal, because if we lose it we're losing an entire species! Nevermind that the species is already effectively gone from the ecosystem!"
Arguments for the existence of the wage gap and similar conclusions: "Women on average make less than men, therefore there's discrimination!" Any such gap is almost certainly due to women working fewer hours on average (because they spend more time raising the children on average), choosing to work in lower-paying fields, et cetera. Since there are so many such factors you'd have to account for to draw a valid conclusion about discrimination on a societal scale from this kind of data, said kind of data is almost entirely useless. If people thought about individuals instead of groups defined by superficial traits, they wouldn't be so keen to commit this kind of fallacy.