Slavery is defined as being involuntarily subjected to another. Forcing me to pick up a rifle and kill seems awfully similar. It is true you have other choices. So did plantation slaves, they didn't HAVE to work, but they would be beat of they didn't. Saying, "you have a choice" is a cold comfort when the alternative is the end of your life as you know it. Finally, the income tax has been argued to be immoral as well. It actually explicitly prohibits an income tax in the text of the constitution. We didn't have one for a long time in this country until they amended it. Forced military participation is morally wrong, when you say I have to go to the military or else, you're saying I am not my own person. On top of that, it's terrible for troop moral, which is a big reason the US doesn't have a Draft anymore. I am a firm believer that the only legitimate use of force is in response to the use of force.