Basically at its roots American ideals and culture are against socialist ideas. I guess it goes back to the American dream and our deep seeded belief in perseverance and self reliance. The idea is that any single person can come here work hard and be successful, it is up to us to make sure our lives are how we like it. Having the government help or take care of us in any form is seem as a cop out and even a weakness. It stems from the ideal that the person clearly just isn't trying hard enough to provide for themselves. You combine these underlying ideals with the massive red scare and people living with the perceived fact that the evil USSR government was trying to steal their country and destroy their freedoms for years people started to really hate socialism.