I never stated you can opt out of mandatory SSA contributions. Damn anti-gubment folk wet dream, so you read what you want to hear.
But, seeing how much you hate our Country, I researched the specific processes on how you can divest yourself of your current or future Social Security benefits. Here's what you can do:
(1) If you have not yet retired, simply avoid avoid applying for Social Security benefits when you do retire. This is a required step to actually receive federal funds, and by not applying, you will get nothing;
(2) If you are currently retired and receiving Social Security benefits, make sure that said funds are issued to you via check. Moving forward, to forego your benefits, simply send your checks back to the federal government accompanied by a letter requesting your removal from receiving such checks moving forward and/or destroy all checks upon receipt and don't deposit/cash them;
The preceding options likely cover 99% of Americans. However, the following option is definitely more apropos for you...
(3) Commit a crime resulting in your incarceration in a jail/prison for more than 30 days. POOF. Your Social Security benefits are suspended while you're picking up lots of prison soap.
So, there you have it. Which option do you intend to pursue to divest yourself of your Social Security benefits?