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.
That's easy. Feeding the poor by robbing money from the productive under threat of jail leads to the economic disaster we are currently in the beginning of. Revisit this line of thought 2-5 years form now.
The problem with that line of argument is that people have been saying since the New Deal. At the moment the economy is bouncing back so obviously the crisis you expect is at least 3 years off. You may well be right but the wait to find out is more likely to be 50 than 5 years.