Unrealized gains are not taxed, long term realized gains and qualified dividends are taxed at the federal rate of 15%, short term realized gains, non-qualified dividends and interest income are taxed at ordinary income rates, which today can be as high as 35% at the federal level and higher still adding in state taxes.
This debt bias is based on the accounting rationale that interest is a tax-deductible cost of doing business while dividends are a non-deductible form of business income.