The biggest problem with Social Security and Medicare is that, with increasing life spans, most of today's recipients end up receiving far more than they contribute to the programs during their working careers.
Example: If you retire at 65, live until 85 and receive $2,000 a month in Social Security, that's $480,000. Few workers have contributed half that.
That's why both programs are rapidly approaching insolvency and have been likened to Ponzi schemes. Young people contributing today are unlikely to get back the money they pay in.
Plus, as you indicate, the federal government already spent your contribution on other programs, so all it can do is create more money out of thin air, making your and my benefit checks—should I ever get one—worthless.