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 didn't see jinni advocating "allowing the poor to starve". I think he believes, as do many, that charities are much more capable than government in providing for the poor since they are much more local, efficient, and accountable.
Forced servitude to provide for someone else is immoral no matter what the person's need is. Voluntarily saying you will help is a completely different matter. Most people are more than willing to help others and around here do so. It isn't charity at the point of a gun, and it isn't charity or moral if you are giving away the products of someone else's life. In short, someone's "need" doesn't give them a right to force you to work to provide something for them.