SD,
1) I did, in fact, offer a distinction between the kinds of infringement of liberty involved in the examples you gave (taxation, public nuisance) and that which you propose -- forced control of (arguably) most aspects of your life for two years of adulthood. I'm sure you're too familiar with the classical treatments of liberty -- Locke, Mills -- for me to have to rehearse them for you here. Suffice to say, such laws as your examples seem, and in any event have been broadly accepted to be, necessary to any minimal social order; whereas the laws you propose manifestly are not, and involve a great many more instances of coercion.
(And yes, you are arguing for coercion. Laws operate by coercion. This is an utterly basic point in political philosophy. But perhaps you wouldn't contest that, and your problem with the word "coercion" was limited to point 2).
Society is "not truly stable," you say -- well, OK. But here we get into real vaguenesses. Society is pretty *dang* stable, and "not truly stable" could be used to justify anything at all. You are obviously very far short of an argument for this particular measure being necessary to preserve a specific type of stability. (Of course, we are on a web forum).
As for the stability being "like that of a stable slave state" -- well, first of all, you just said it wasn't truly stable, so you're contradicting yourself. Second of all, your assertion is laughable to anybody familiar with the history of different societies in the world, including slave states. Ours is among the freest organized societies ever to exist.
You can assert that I "can't do philosophy," but you should provide actual arguments.
2) "Scale doesn’t matter to principles. If something is right or wrong by principle it doesn’t matter the scale. If x is wrong by definition, it doesn’t matter if there is a lot of x or not much x."
This is just more casuistry. You are misdefining the principle so that it contains too many cases. You are right -- in capitalism, one must work (and this is fine and moral), although one is unlikely to actually die of starvation or exposure if one does not. However, once again, the choice faced by individuals entering the military is not (or, you have not shown that it is) to enter the military or not to work at all. Often, it is to enter the military or to work at a worse job and live a worse life. So, as in the snickers example, "the alternative is fine."
In brief, you are too broadly defining the "principle." Immoral force is when the person must choose between life and death, maiming or keeping their limbs. Offering them the choice between an apartment and a house does not constitute immoral force, even if the house is very attractive.
Even to the extent, by the way, that there were people who had to join the military or starve, your solution wouldn't solve a thing. They would still be forced to join the military, and presumably they would be forced to stay there for more than two years (or return to starving).