Social Security is a government-run pension program, and Medicare is a government-run insurance program that provide services directly to individuals.
Taxes imply that you, as an individual, will never get your money back because you are paying into the collective good as part of the social contract. Payroll taxes are directly tied to a benefit that you receive, making them premiums.
Actually, you're completely wrong.
First off, while politically it would never happen, the Government could end Social Security and Medicare any time it wanted to. There is no legal obligation for the Government to pay anything. So it categorically is NOT a pension.
Secondly, as I already pointed out, the linkage between taxes paid and benefits received is at best fuzzy. At the lowest levels of income (below $359,520 in indexed earnings over your 35 highest pay years), each dollar paid in results in six times as much benefits as at the highest levels of income (above $2,525,460 in indexed earnings). If you earn over $72,156 per year, then effectively all you are doing on the reducing the amount of time it takes to reach maximum benefit levels below 35 years of work. Similarly, once you've been working 35 years, all you might do to improve your benefits is replace a lower valued indexed yearly income with a higher totaled yearly income.
Thirdly, unlike any actual pension, Social Security benefits can be subject to income tax if you have other income. While some types of retirement benefits are subject to tax, that is entirely dependent upon whether the pension was funded with pre-tax or post-tax income. As a general rule, if the money used to fund your retirement benefit lowered your taxes when you funded it, it'll be taxed when you receive the benefit, but if not then not.
Fourthly, another little dirty fact arguing against considering Medicare an insurance program is that unlike Social Security and the employer portion of the Medicare tax, the employee portion of the Medicare tax is uncapped. Social Security taxes (both on the employee and employer) and the employer portion of the Medicare tax are only levied on the first $118,500 of earned income. The employee portion is levied on it all. That 1.45% comes out of every dollar of wages, regardless of whether it is the first dollar or your ten millionth, and yet it doesn't matter how much you paid in Medicare tax when determining your Medicare premiums. Part A is free, presuming you worked at least 10 years and premiums for Parts B, C and D don't depend on how much you paid in Medicare tax. Part B and D premiums might be higher if you have sufficient income (from whatever source) to trigger surcharges (i.e., added taxes) to the premium.
I like Social Security and Medicare, but the part that comes out of our paychecks is absolutely, positively, 100% a tax and not a premium for a pension or insurance. Granted, to make the programs more politically palatable, they been paraded around from the beginning as if they were simply a Government-operated pension/insurance plans, but they aren't and never were.