SSI, as a tax, and as a percentage of income, the poor guy pays pays a larger percentage of his income, than the rich guy, towards this tax. The poor guy pays a larger percentage of his income to the nobamacare taxes, than the rich guy. The poor guy, pays a larger percentage of his income for excise taxes, than the rich guy. The "benefits" are not relevant here, though they do not justify the disproportionate tax assessments.
You forget that 48% of the people pay no income taxes. The rich guy pays huge excise taxes on jewelry, communications and expensive items such as yachts which a poor man can't afford. He also pays huge amounts of property taxes on possibly several expense homes and taxes on his expensive cars. He pays large amounts of taxes on airplane tickets and vacations. He probably donates his puny S.S. checks to a charity as he doesn't need them. He would have to pay taxes on his S.S. checks if he didn't donate them. We haven't even mentioned the income taxes that would be much higher than a poorer mans, that is if the poorer man paid any at all.
Perhaps you would like to see no cap at all put on S.S payouts per year.You would let the rich man pay 6.8% on all his salary, lets just say 2 million dollars a year, and receive a $3,400 a month for the $136,000 he put in every year till he hit 70 years old. He would have put in $5,440,000 into Social Security over a 40 year work period. He would get a $3,400 taxable check each month till he dies. That sounds fair.