There are only enough full time jobs for around 50% of Americans...
There is something called an unemployment rate... it means that there are fewer jobs than there are job seekers... so there is a substantial percentage of people out there without work, living in poverty, who do not shoulder the blame...
Sure, plumbers can make reasonable money. But can we have a nation of specialists? No. They only represent a small percentage of job openings in the country. The fundamental tendency of capitalism is to reduce more and more jobs to unskilled labor, as it increases competition among workers, driving down wages and pushing up profits.
Yeah, you might be able to live comfortably on 25-45k. But try doing that in an expensive area, with a stay at home mom raising two kids, while saving money for their college tuition, setting money aside for retirement, taking the occasional family vacation, maintaining one or two cars and paying for all the gas (can easily hit 1000/mo for two cars), paying a mortgage, property taxes, etc...