Why should those who work for a living be subject to higher tax rates than those who reap their livelihood from speculation (often at the expense of others)?

Peasants toil inefficiently on tiny plots of land, in a form of disguised unemployment similar to that seen in rural China.

Creating a fairer and more efficient tax system, by eliminating the special treatment of capital gains and dividends, is also needed. Why should those who work for a living be subject to higher tax rates than those who reap their livelihood from speculation (often at the expense of others)?