Modernman,
Given your silly "correction" in 42, I am not convinced if your presence here is to argue objective truths. Most moderns are disinclined to do so, and your screen name makes modernity your distinguishing characteristic, which you seem to wear proudly. But here it goes.
Your moral duties are not limited to contractual duties, which arise from consent. Most people, for example, are free from contractual obligations to not murder anyone outside of your family, yet we have a duty not to murder.
Your second argument, regarding supposed justification of socialism, contains no logic. Most errors, and socialism is no exception, refer to objective truths as they reach wrong conclusions. This is no reason to discard the truth. For example, if an airplane is designed badly and falls on the ground, that would not falsify the laws of gravity. Where is the socialism's error? Socialism imputes a situation of dependence where none objectively exists. Generally, a poor man's life does not depend on the rich man's possessions. Since there is no dependence, there is no duty to distribute wealth. In the situation of pregnancy, the baby's life is directly dependent on the mother's body, so the motherly duty is objective rather than imagined. Similarly in the contrived example with the kidnaping and the gurney.
Sure. But without the mother's consent to such dependence, she has no moral duty to continue such dependence.
A moral duty cannot be forced upon you by the actions of another.