Can you explain to me whether/why communism is bad? Since I've always heard communism is the devil, but it kind of sounds like repressive institutions ceasing to exist and production being prioritized by needs, is actually a good thing. Or does anti-communism come just from rich people wanting to stay rich essentially?
Communism, in theory, isn't bad. But neither is capitalism.
The problem with communism, or left wing ideology in general, is the lack of incentive to work hard. Why work extra hard on that business venture, enduring sleepless nights to meet that deadline, when Joe Blow down the road gets rewarded just as much as you for flipping burgers part time. However in a perfect world, if everyone agreed to do their very best, it could maybe work. The communities would have to be small enough to feel a sense of camaraderie. Something around 150 people per community, see Dunbar's Number. Also consider that small benevolent communities are vulnerable to attack from an aggressor.
Capitalism, however, compensates for our inclination towards leisure. Three people shipwrecked on an island will instinctively engage in capitalism. Bob will fish all day, Sally will collect firewood, and Joe will build shelter. Then they'll trade the products of their labor with each other. Sure, they're probably good friends (community<150) and they'll probably share with each other regardless of productivity. But if one of them decides to be a lazy asshole, there's no gun pointed at their head to produce more, or share with the unproductive members. Capitalism does not preclude charity.
Each of these systems could theoretically work, but unfortunately society doesn't exist in a vacuum. We don't currently have free market capitalism, despite what most people think. Corporations are a result of government intervention. Corporations are granted freedoms that exonerate members from accountability, backed by the state at gunpoint. Politicians grant freedoms to corporations, corporations lobby (bribe) politicians for favors, and we watch the puppet show. Successful communism would require the elimination of sociopaths and tyrants. Successful capitalism would require the elimination of big government. Neither of these are plausible without revolution, and even then, the rabbit hole goes so deep even this wouldn't be enough. You can't win by playing the left vs right game. The house always wins.