As a trader, assuming that you are reporting your expenses on Schedule C, and your "income" on Schedule D, you are not subject to FICA tax, since it is not considered "earned" income.
The drawback of this is that you cannot claim your health insurance deductions or retirement plan contributions as deductions. Health insurance can only be claimed on your Schedule A, for the amount that is in excess of 7.5% of your adjust gross income.
If you form a corporation, you can pay FICA, and deduct the above, but the details are beyond my basic knowledge.