This is misleading. You do NOT need to pay US self-employment Social Security taxes if you are an expat abroad and you pay the self-employment taxes in the country where you live. I live in France and pay 22% self employment taxes on my earnings. The Totalization agreement between France and the USA means that I do NOT need to pay the 15% US self-employment tax because that is called "double taxation". Below is information from the irs.gov website explaining this concept.
International Social Security Agreements
The United States has entered into social security agreements with foreign countries to coordinate social security coverage and taxation of workers employed for part or all of their working careers in one of the countries. These agreements are commonly referred to as Totalization Agreements. Under these agreements, dual coverage and dual contributions (taxes) for the same work are eliminated. The agreements generally make sure that social security taxes (including self-employment tax) are paid only to one country.
If your self-employment earnings should be exempt from foreign social security tax and subject only to U.S. self-employment tax, you should request a certificate of coverage from the U.S. Social Security Administration, Office of International Programs. The certificate will establish your exemption from the foreign social security tax. You can get more information about the Totalization Agreements on the Social Security Administration's web site.
To establish that your self-employment income is subject only to foreign social security taxes and is exempt from U.S. self-employment tax, request a certificate of coverage from the appropriate agency of the foreign country. If the foreign country will not issue the certificate, you should request a statement that your income is not covered by the U.S. social security system. Request it from the U.S. Social Security Administration. Attach a photocopy of either statement to your Form 1040 each year you are exempt from U.S. self-employment tax. Also print “Exempt, see attached statement” on the line for self-employment tax.
See the “Self-Employment Tax” information in IRS Publication 54, Tax Guide for U.S. Citizens and Resident Aliens Abroad, for more detailed information about self-employment tax for U.S. citizens and residents abroad.
