During my college years when I was sort of floating around politically after being a traditional 2000s liberal in high school, this was the main thing that turned me off of the "leftist/socialist/dsa" crowd.
Liberal, Democrat, Conservative, Republican, all those things that existed prior to 2010, all had members I found reasonable with just different life experiences and such.
Every. Single. Fucking. Leftist. That I knew, and I knew a lot, were the most ungrateful, selfish, entitled, disloyal to their friends, quick to anger, impatient during disagreements, dismissive, often violent, emotionally unstable, lazy, pieces of shit. The actual messaging of leftism appealed to me at that age because I was young and naive, but what really turned me off even back then was just the people.
They will qualify it with all sorts of bullshit like "if you had a heart you would be miserable too" or "i'm only angry because i'm not privileged like you!" blah blah blah, but it doesn't matter. At the end of the day i'm not going to believe you have the tools to run this perfect kind utopian society in a completely selfless manner if you can't even come close to handling your own life that way. Running society is a million times harder, so talk to me when you can manage your coworkers and classmates without flying off the fucking handle and huff and puff anytime things don't go your way, you'll be dealing with a LOT more if you're running the country.