Soc Sec and Medicare ARE NOT "accounting gimmicks".
The use you are making of them in this argument most definitely is an accounting gimmick. The separation of taxes into income tax, capital gains, and Social Security/Medicre tax may have legitimate functions, but considering whether people are paying their fair share is not one of them.
There is only one way to evaluate that:
1) Calculate the total federal tax liability of a person in given circumstances.
2) Calculate the person's total income for the same year.
3) Divide the result of 1 by the result of 2.
This will give us the percentage of the person's income that the government takes in taxes.
Also, the only way to consider whether it's appropriate to raise a given person's taxes, assuming taxes need to be raised, is this:
1) Calculate the person's after tax income (2-1 in the above).
2) Analyze what the person will have to give up if his/her taxes are increased, not just as a dollar amount but in terms of purchases.
If the person will have to give up a little investment in financial derivatives, his taxes can be raised with no significant harm done to anyone.
If the person will have to give up buying a vacation home or taking a round the world cruise, his taxes can be raised with minor harm to his lifestyle.
If the person will have to give up medical care or a college education, raising his taxes will do serious harm.
If the person will have to give up food, raising his taxes is simply unconscionable.