Capitalism has given a lot of people out there a raw deal: low wages, increasing gap between the rich and the poor, home ownership is out of reach to many, healthcare is unaffordable to many, having a family is prohibitively expensive, we own almost nothing and rent almost everything, even basic necessities like food, water and clothing are painfully expensive. What's more, when you look at the systems in place today, it appears that these aren't bugs, but features.
I'm a socialist because I believe that society ought to use its collective power and money to guarantee all of its people a minimum of the basic, essential things that they need to live, by subsidizing food, water, shelter, clothing, heat, electricity, data, education and healthcare.
Outside of those crucial things, capitalism is just fine, as long as people are being paid fairly for their time. And, as we've all seen, capitalism needs strict rules and guard rails to make sure that workers aren't being constantly exploited. If capitalism was working well for everyone, we were all getting paid fairly for our time, and people could take care of their needs (not to mention their wants), then nobody would have any reason to care or complain about capitalism. But sadly, as it is today, capitalism is just not working for a lot of people, and many people out there are not even having their basic needs met (even despite getting an education, taking out loans, getting a job, getting a second job, working hard, etc.).
To me, creating a prosperous and happy society is much more complex than picking capitalism or socialism, and some mix of both is probably the best of both worlds.