Giving consumers more money works to boost demand, but you don't need more demand except in cases where the economy is in recession. It's more a special case than the general rule.
All economic growth in the long-run comes from innovation, resources, and capital deepening....IE, the supply side. Not all tax cuts are equal, and if you are going to go for a supply-side tax cut, you should target the people who actually are most likely to produce more with a tax reduction. To give a labor economics example, men are not as sensitive to the tax rate as women are. Men just work per their social-norm required hours. Women are more likely to have a decision between working part-time, full-time, or not at all, and are more likely to work when the tax rate is lower.
Either way, though, reducing tax cuts on the middle class would be considered less important than cutting taxes on innovators, savers, and investors.
Most conservative economists will point out that the phase-outs of government spending create marginal tax rates close to or over 100% for lower-income families, but that's not the middle class either.
I hope you're just saying that since it's the basis of supply-side economics and not something you actually believe. In the economic literature, supply-side economics is given about as much credibility as homeopathy is by Western medicine.
Not really. This is just a Democratic political attack. There's no one that believes in the extreme claims that tax cuts pay for themselves, but that's totally different from everyone assuming tax cuts are a bad idea and tax hikes pose no problem at all.