1) Dividends are already taxed once, at the corporate level. What you are suggesting would mean that dividends would be double and triple taxed.

Per individual, they are taxed once. Like every dollar that passes through a variety of hands, it is taxed by the hand, not in some single absolute sense. Perhaps it's the anti-collective hangup that prevetns you from seeing this?

2) Incentives matter. People (and corporations) would change their behavior to negate the increased tax.

Not an increase, just a return to normalcy after W screwed it up. Incentives DO matter, though, which is why we need to incentivize business owners to invest in their business rather than pay themselves beyond the dreams of avarice.

3) Incentives matter. Investments are the driver of economic growth. Punishing investments & investors will result in reduced growth.

Good-paying, more secure middle class jobs are the biggest driver of economic growth. In aggregate, we are the big spenders. And Social Security, which keeps the elderly not only out of poverty, but spending. Most seniors live on at least 50% Social Security. Ask any senior below the top 5-10% how their spending would be affected without it. As an example, my mother lives on $3k/month, about half investments (mostly bond interest) and half Social Security. Without SS, she'd move from the middle class to the lower middle class or even the poor.