NO.
They don't.
The Social Security withholding is a contribution to a national public pension plan. The promise is that it will be returned. That's NOT a tax, any more than your 401(K) or IRA is a tax.
Same thing with Medicare. That's also not a tax. It's a contribution to a national health care program for Seniors, and again, at a certain age, the promise is that it comes back to you. It's a public insurance plan, and it's NOT A TAX.
When is a tax not a tax? When it's a government-mandated "contribution" of the first 15% of your earnings to a government monopoly "savings plan" Ponzi scheme.Social Security takes money when you are working, and pays back "more" than you paid in - in devalued dollars after the government has done its inflationary dirty work over the years. But I guess it's not a tax as long as the government pays back something . . .
I must buy car insurance to drive: it's the law, and there are criminal penalties for violating it. But that doesn't make it a tax.
The fact that the return is poor changes nothing. The fact that the government has borrowed and squandered most of it changes nothing. The fact that it's mandated changes nothing.
If you want to be on the side of politicians who make a shameful claim that "everybody who works pays federal taxes," that's fine with me. But it's a lie: 1/2 of the people who work in this country make no contribution to America. That is the fact.