Because Karl Marx said socialism is good, and they determined Karl Marx is bad, therefore socialism must be bad.
Other way. They determined socialism is bad first since that gives a real alternative to capitalism.
It doesn’t need to be an alternative. It’s a really effective way to regulate capitalism by standardizing and socializing private industries like education, police, fire, roads, internet access, healthcare, etc.
Socialism is the workers collectively owning the means of production, everything else is just details. (Well, the anti-heirarchy bit is important too, especially to keep the means from falling into something that isn’t just capitalism with extra steps, but complicated)
It is innately opposed to capitalism as a result. What it isn’t innately opposed to is a market economy.