I think it has a bigger deterrence effect with non-capital gains income. Once you start getting in the higher income tax brackets, it isn't really worth it to put in more hours for additional income when 50% of it is taken in income tax off the top. That's how I look at it at least.
Clarification - I am not making any claims as to whether I support this tax level or not. I am just saying it doesn't discourage me from trying to get ahead.
That distorts my willingness to employ lower skilled help. I change my own brakes because the $250 in labor/markup that I might have to pay costs me $500 to earn. If I don’t have a productive way to earn more than $500 in exchange for the small time savings, my family is better off with my changing brakes than working on something else and a mechanic doesn’t get 2.5 hours of pay and some shop loses out on their cut. Same story for lawn care and other tasks that could easily help support employment of some workers.
If they told you that if you volunteered for government on saturdays, they would exempt you from income tax altogether, would you do it?
Also, as long as the tax rate is less than 100%, the reward will be higher than 0, which is what you get if you don't invest at all.
But what if you are investing in stocks or corporate bonds or a broadway play or a promising health technology company like Theranos? There is a non-trivial chance that your reward will be less than 0 - and it could even be a complete wipeout. The low capital gains rate is meant to encourage people to put money at risk rather than sit on it.
Imagine we bet $1 on a coin toss. The expected value for either of us is $0. Now imagine the winner is required to pay 10% tax on his proceeds. The expected value becomes (-$1.00 + $.90)/2 = -$0.05.
Also, as brorfred pointed out, capital losses are deductible, afaik.
To increase wealth the lower tax will have to mean more money under the control of the individual. It doesn't guarantee savings and investment but it makes it possible. For the portion that is taxed, you don't control consumption versus savings, you're locked into the same outcome as everyone else.
1. A lower tax for everyone, including the super-rich.
2. A lower tax for the poor/middle-class, but a progressive and higher tax for the rich.
The first, lowering the tax-rate for everyone, only really helps the super-rich in the first place. The poor currently pay relatively few taxes. Lowering the tax-rate across the board will result in the rich taking home a larger absolute increase in wealth, so it will shift further spending power to the rich.
The second is a common enough socialist talking point, and if that's what you mean to talk about, saying "lower taxes" is a terrible way to do it and will put socialists against you.
I don't really see how you think lowering the tax rate will increase individual wealth for anyone not already doing well. If we reduce the tax rate, that means public transit, healthcare, and schools (all heavily tax subsidized) will suffer, and any change in those disproportionally impacts the poor.
I know you're not literally saying "fuck the poor, they pay negligible taxes now, so let's cut taxes and raise their healthcare costs by crippling the government", but talking about cutting taxes across the board really isn't far from saying "give the wealthy lots more money, the poor a tiny bit more money, and cut funding on social safety nets that only help the poor."
Which one wins is something to figure out empirically, but look at the fact that europe has more leisure than the US does, even at the same level of income.