Because taxes take money from productive sectors and redistribute them to the less productive. Not sure where the ideas about taking money from some people and giving it to to others came from. No person is keeping their money in a chest.
Government spending is the least efficient form of spending, and governments in the past few years have spent too much. Look at how much debt local, state, and the federal governments have accumulated.
By lowering taxes business have more money, and thus are more secure - they can handle an uncertain future better. So if a business has 100k in savings it can then hire another worker, and be ok if the economy goes down a little bit. If they only have 10k then they won't hire a new worker because it could put them out of business if the forecasted sales are wrong.
But you have no idea if the rich will actually invest that money in the country, and if they'll do it now. Currently it looks like the answer to both of those questions is no.
As for government spending being inefficient, I know that's a common theme, but a lot of studies have shown that it isn't so clear cut. Sure, there are examples where that it is actually true. But most of the time people just use anecdotal experience and the conclusions are wrong.
In the UK, despite everyone complaining of the NHS (the national health service), it actually performs a great job.
As for if it's fair or not to take money away from the rich to give it to the poor, personally I think it is. Not because I want a communist society (far from it, I think communism has no basis in reality) but because of the old saying: "It needs money to make money". For example...
A rich family has already covered all their primary needs with their 20%, and with another 30% they cover the less important stuff. Since they have no use for the rest so far, they may either invest it or put it in a bank. Hopefully they'll get extra revenue from it which they can invest again, and so on.
The poor family, instead spends 100% just to pay for primary needs and a few non-essential goods. They are not left with anything to invest. If the want to get a new house or start a business they need to borrow money. That's basically saying that the poor get taxed for trying to get a house or start a business, so compare to those who are rich they need to earn more from that business for the net revenue to be positive.
But even if you don't think it's fair, it still helps the rich to give money to the poor, though only in the long run. A lot of poverty means more criminality. A lot of sick people means higher chances of contagious diseases. The rich gets a benefit from making sure that the poor are not too poor.
But anyway, these last two points are personal, and I understand if you don't agree. In either case I still think that giving money to the poor in an economy downturn is good to start up an economy where people are weary of investing.
Government spending is the least efficient form of spending, and governments in the past few years have spent too much. Look at how much debt local, state, and the federal governments have accumulated.
By lowering taxes business have more money, and thus are more secure - they can handle an uncertain future better. So if a business has 100k in savings it can then hire another worker, and be ok if the economy goes down a little bit. If they only have 10k then they won't hire a new worker because it could put them out of business if the forecasted sales are wrong.