Most people want to be treated fairly. And most people think that others like them are trying to play fairly as well. So, when you're brought up that hard work and going to church and being independent will be rewarded in this life, or certainly in the next, then you want a system that makes those things the rules.
When people are "given" things, they're not obeying the "hard work" rule.
When people are atheists or Muslim, they don't go to church, so they're not obeying the that rule.
When people aren't "independent" businesses, they're getting rewards or are too cowardly to be out on their own. They don't deserve as much from what should be a "fair" system.
When people are taxed above the level that the Founding Fathers ® intended (and they didn't have an income tax or inheritance tax, thankyouverymuch), then the system is taking from people who are playing by the "true" rules and giving to those who aren't.
So that's the mindset, I think. I bought into a lot of it (but by no means all of it) as a youngster. It is appealing if you like to see things without shades of gray or confuse a model of reality for actual reality....
Of course there are contradictions. "Keep your dirty hands off my Medicare!" "I'm on a fixed Social Security income! How dare you cut my COLA!" "I paid for my benefits! It's not welfare!"
As long as the mythos taught in school and in the media is that this country was founded by independent individual white men who were interested in nothing more than their Freedom ® and that they fought federal government Tyranny ® at every turn, then continuing or expanding sensible programs that "promote the general welfare to ourselves and our posterity" ® will be an uphill battle.
Myths are often much more powerful than reality.
My $0.02. FWIW.
Cheers,
Scott.