A minimum income tax?

Ok, here’s something to ponder from my personal ‘Must be off my meds’ inner thoughts… One of the obligations we have as citizens and legal residents in the United States is the paying of income taxes. Some people pay a lot of income taxes and some pay none at all, yet we are all equal under the law. So, it seems to me, there should be a minimum tax levied unto all who do not earn enough to pay any income taxes. They’re still citizens and legal residents with all the perks afforded to others who do pay income taxes… why shouldn’t they also share in the burden of supporting our government via a minimum tax