If however, you view the arts, the environment, social welfare, public works and the like as worthy causes also,
I'd argue that we not only spend plenty but far more than enough money to such causes, but the other fact is that the military requires a government to direct it--whereas the government does not have the duty, nor the right to spend money that belongs to someone else on what it thinks are worthy causes.

That's not even counting the money the government wastes on little specialties like Piss Christ and The Holy Virgin Mary. After seeing public housing and public art, I'd rather pass on the government's other 'worthy causes'.

That, in a nutshell is the argument against Reaganomics. If you give the richest of the rich more money through tax breaks, it all relies on them as the individual to reinvest it into the market. However, most follow the logic that you pointed out yourself, in that they spend the money on themselves and the trickle down effect runs dry before anyone on the lower levels actually gets saturated.
Except that a) history has proven that enough of them do get the money back into the economy, and b) the 'richest of the rich' do not live in a vacuum. Spending money on themselves still means that people get employed, and goods and services are bought.

Most importantly, tax breaks do not 'give the richest of the rich more money'. To steal less money from someone is not to give them anything.