Certainly they can, but as long as they keep collecting the money through taxes it is an immoral use of force.
Saying that collecting taxes is immoral doesn't really advance your cause much. Most people think its immoral to allow the poor to starve and thus collecting taxes is the lesser of two evils. What you need to do is either make a moral case for allowing the poor to starve or stop complaining about taxation being immoral.
I think there are far easier and cheaper ways to prevent starvation than through forcing someone to pay taxes and then spending a small portion of those taxes on actually helping people, while the vast majority of it goes into an ever expanding bureaucracy or to fund wars etc.
Can you make the moral case of how it is moral to have an income and pay taxes if you know that a part of that money will be spent on mass murder?
Anyway, starvation is normally solved by technology, not by government spending.