My understanding is that the qualified dividend tax rate is technically a different thing than the capital gains tax rate, and they only happen to have the same value - not that that's very important to this discussion.
More importantly, this is partly incorrect as it applies to employees. Employee wages are an expense deducted before corporate profits are taxed; I believe (though I'm less confident) that in the case of profit sharing money going to employees could face double taxation.
Most importantly, though, "double or triple taxation" is misleading. Every time the money is taxed needs to be taken into consideration, to be sure, but the ultimate question is the overall rate, not the number of passes. (Please, please, please QUINTUPLE TAX me at 0.01% per pass...)
With loopholes and exemptions and deductions and sliding scales and different rates in different jurisdictions and everything, that's not a simple question, unfortunately.
Oversimplifying, though, for a single example...
Consider the following individuals in a State (fictional, if necessary) with no corporate or individual income tax and no tax on dividends, interacting with a corporation in the same State. The corporation turns a profit (income minus expenses) of $2 million/year, some of which it saves year-to-year and the rest of which it pays out in dividends.
1) Middle-class employee of the company.
2) Super-wealthy stockholder in the company.
3) Minimum wage employee of the company.
4) Middle-class stockholder in the company.
1) Makes 75000, takes standard deduction of $6100. Pays $14492 in income taxes, plus $9300 FICA (half of which comes from employer, but it's still a tax on the employee's income) for a total of $23792, or an overall tax rate of about 31.7%
2) Assuming their income is such that they can be reasonably assumed to be paying the top bracket on their average dollar (this person is really making a ton of money, and it's not all coming from this company): A dollar of corporate income that will wind up in this person's hands is taxed at approximately 34%. The $0.66 cents per dollar that he's receiving is then taxed at 20%, meaning a total of 47.2%.
3) $7.25 * 40 * 52 = $15,080 / year. They pay only $901 in income tax, but the $1870 they pay in FICA brings it up to $2771, which is about 18.4%. They may or may not qualify for assistance under one or more of our various current means-tested systems.
4) Profit within the corporation is taxed the same as for the wealthy investor, but now the $0.66 cents per dollar income is taxed at only 15%, for a total of 44% instead. This assumes they are making more than $36,250, which seems fair - but if they are not, the tax rate on the dividend income is 0%, so they are paying in total only the 34%.
I'm not making any particular point regarding what tax policy ought to be, just trying to shift the focus to numbers that are more meaningful.