Except the world is not black and white, and leaders always make subjective determinations according to their own personal and political needs rather than what is best for everybody. IMHO, that is one reason why redistributing wealth by the gov't is immoral, it requires action based on the values of some of us to the cost of others.
As does collecting tax to fund an army. Is that also immoral?
No, national defense and security are important duties of gov't that individuals cannot do themselves. Every citizen benefits equally from a strong national defense, and it is therefore moral. Not to mention the fact that such respnsibilities are specifically defined in our Constitution.
There's a difference between taxing people's money for the benefit of all as opposed to spending that money to the benefit of only some citizens. There are exceptions, like supporting those who cannot support themselves, and those who need temporary help, like the people who've lost everything as a result of the tornados or can't find work due to the recession. But arbitrarily deciding what's fair and redistributing wealth from those who earned it to those who didn't just because they don't have as much is immoral IMHO.