The deductible portion of self-employment tax is equivalent to the portion of a non-owner employee's Social Security and Medicare taxes that are paid by the employer and end up not being part of the net earnings of the employer. IRS Pub 590-A makes this explicit by indicating that your compensation available to support an IRA contribution is your net profit from self-employment reduced by the amount of any self-employed retirement deduction and reduced by the deductible portion of self-employment taxes. Even if you were permitted to decline to take the deduction for the deductible portion of self-employment taxes, doing so would not increase the amount that you would be permitted to contribute to an IRA because the deductible portion of self-employment taxes is explicitly treated as not being part of your "compensation."
