It's manufactured hate.
It benefits those in power to make average citizens fear socialism.
We already live in a system with numerous socialist programs. Many of the people who have been brainwashed to hate the concept of socialism already benefit from some of these socialist programs.
As with pretty much everything in life, you have to find a happy medium. That goes for socialism too. A full on 100% socialist society may not function well. Just like how we're witnessing the failures of the ultra-capitalist society we live in.
But the brainwashed don't want to meet in the middle. They fear socialism and don't want any trace of it in our society....despite the fact that there are already many socialist aspects present.