I believe that the main problem with socialism and hard Left wing ideology overall is that it's so attractive in theory but fails to work on practice. It creates a very real danger: since the allure of this ideology is so great, it can attract a lot of people to it (especially young people who are idealistic and full of energy), but since the building of socialist paradise always fails, it can do a great harm, and more people get lured into socialist nets, more harm would they do.
I mean even I understand the attraction of socialist ideologies. They speak of social justice, equality, brotherhood (or sisterhood), end of exploitation...Who would not want all of that, really? When you read Marx or Hegel, or any other Leftist philosopher, their theories even make sense somewhat. When you read sci-fi socialist utopias (like some novels by Ursula le Guin), you wanna live in that kind of society. So no wonder many young people worldwide (and in US especially nowadays) are still so much attracted to socialism and believe that Karl Marx was right all along despite socialism failed literally everywhere where it was tried - from Soviet Union and China to Cuba and North Korea.
But of course, 'it was not a true socialism', these young socialists of a new generation are telling us. Only where is their 'true socialism'? It seems it exists nowhere but in their dreams and in the papers of their theorists. Those young people remind me of some Christians or Muslims who are fiercely defending their religions by saying that 'Inquisition was no true Christianity and sharia law isn't true Islam'. Good for them, but again, when you ask them what is true Christianity or true Islam then, it seems that these 'true concepts' do exist also only in the imagination of their devotees or on the pages of Bible and Quran, but nowhere in the real world. I'm making two points there: first, that socialism indeed reminds me of religion a lot with this regard, and second, that it works only in theory but never on practice.
Indeed, whenever socialism was tried, it failed. In most of the cases (USSR, China, Cambodia, Cuba, North Korea), socialist paradise quickly degenerated into totalitarian dictatorship. In almost all of those cases, grand bloodshed ensued, and millions of people were executed and massacred by 'benevolent socialist regimes'. It seems that all this should teach even the dumbest of people that socialism should never ever again be tried, that something inherently wrong is with this ideology. But nope, the allure of this toxic ideology is so great that people are falling for it over and over again.
Also, note that nowadays it's mostly Western (and primarily American) people who are falling for hard socialism. Americans never lived under socialism, never experienced it on their own skin. Indeed, US was a capitalist paradise all the time, the entire opposite of socialism. As such, US was instrumental in bringing down USSR, the main domain of socialism. So now, being fed up with their capitalist paradise (or realizing some its downsides they were blind to before, alright), Americans crave for its opposite to 'fix its failures'. Perhaps, some of those young American socialists are even stupid enough to seriously believe that 'fight against socialism' was just an excuse for 'aggressive American imperialism', and socialism is indeed not as bad as it was painted in the West. Quite bold statement for people who never lived in socialist country but still dismiss warnings sent countless times by me and other expats from former Soviet Union who learned on their own skin what 'true socialism' was. But alas, it seems people are unable to listen and to learn on others' mistakes, so perhaps the only way for the Westerners to learn of the evils of socialism is to try it themselves.
So perhaps the faster Demon Rats would turn US into USSR, the faster Americans would wake up and rebel against this bullshit. If they would still have any freedoms left to do it, though - for now, it seems that all kinds of freedom are deteriorating in US at the speed of light, and, indeed, people living in totalitarian socialist paradise, have no freedoms at all. But alas, Americans brought this shit upon themselves, they were warned. But they allowed the media propaganda about fictitious 'racist evils' of the Orange Clown to dupe them, and fostered real Leftist totalitarian evil under their very noses. So now they would learn what is true socialism, or its corporate version at least, (since Big Tech and other largest American corporations would never allow real socialism to emerge in US but alas all these young American socialists duped by media propaganda are unaware of that) on their own skins. Good luck with that.
But why does socialism always fail whenever it tried? I don't have a sure answer for that, but my political scientist's and philosopher's hunch is that socialism (and any hard Left wing ideology as such) is built heavily on totally unrealistic assumptions about human behavior. It doesn't take into account all complexity of human nature. More precisely, all social theorists for some unknown reason assume that literally EVERYONE should be interested in building of socialist paradise once they learned how beautiful it is. In reality, it turns out that many people aren't. Some of them are pretty ok with 'old unfair system' and don't want to change anything and even to try to achieve social justice. Others might not mind socialist paradise but are unwilling to put any efforts into it and to pay their share, and, hence, are freeloading. So what to do with all these people? The only solution socialists came up with is TO FORCE them to comply with new socialist rules. Hence, in its very basis socialism is based on denying of individual freedom, on forceful implementation of socialist ideals, and on getting rid of all dissenters. Why? Because social theorists didn't even account for the very existence of dissenters in their theories - they just ASSUMED that everyone should want socialism. But if some people don't, then they should be forced to socialism. Is it any wonder that socialist regimes always degenerated into ugly totalitarian dictatorships?
There is another reason for it, though. Socialist theorists failed to account also for human power greed and selfishness. They somehow again baselessly assumed that human greed and power hunger would automatically disappear once 'new social order based on justice and equality' emerged. However, humans are still humans, no matter the regime they live in. Better environment doesn't necessarily makes better everyone who lives in it. Humans are still flawed and corrupt. And if you fail to account for this imperfection of human nature, every your dream society, however fair and just, would eventually be corrupted.
Our democratic societies at least are based on the system of controls and balances which are designed to make our leaders accountable to people who elected them. In socialist regimes, which are usually dictatorships, there is no accountability of the leaders. For example, in USSR it was really believed that if private property was largely abolished, it would stop human greed, and leaders would genuinely care of their people. Alas, they didn't take into account power greed which is present irrespective to any proprietary or monetary factors. Socialist leaders perhaps don't accumulate money as capitalist ones, but they accumulate power nevertheless. And if they are not accountable to their people, it's very dangerous.
Our democracy is also based on individual freedoms and rights. Socialism denies both. In socialism, everyone who doesn't want socialism should be forced to accept it 'for their own good', and also be ready to make any personal sacrifices for the 'greater good' as a side effect since common, group well-being is always valued ABOVE individual well-being in every social regime (and even social theories as well - as I said, social theorists craftily avoid any moral dilemmas about that by assuming that 'all people should want socialism'). But society is made of individuals. Individual well-being and happiness is the basis of the common well-being as well. Indeed, how could you build a solid house of broken bricks? But this is what socialists try to do. That's why they are wrong, and should be stopped.