I think it's clear that Rangel and the rest of the Democrats have absolutely no plans to *actually* institute a draft. I think the point, however, is that a reasonable threat of a draft sure would make people evaulate how much the support the war and future possible conflicts. I think the point is that most Americans would not support a draft even if it were the case that a draft was necessary to keep up our troop levels or increase our success. That is, they want to have the war, but not if war comes along with the draft. By making people choose between no draft at all and war & draft as a package, people are made to decide exactly how important the war is to them.
It seems to me if a war isn't worth a draft then it must not be very important. And as others have pointed out, people who support the war but are not currently serving themselves (or do not have their own children, siblings, friends, nieces, nephews, etc.) serving, would have to decide how important the war is to them. Is it worth the risk of their own life--or the lives of their children? Of course for some people the answer is yes. The point, however, is that for many people who currently support the war, the answer is might be "no"--they might rather walk out of Iraq today than risk their child's life (or their own).
If someone is of the opinion that they are very pro-war so long as there is no draft, and their opposition to the draft is largely based on their own concern for themselves or their loved ones that seems problematic to me. If it ain't worth risking my life over, then I don't feel I have the right to support others being forced to risk their lives over it.