Sorry for confusion, second marginal was mistake, I meant even marginal cost is zero, actual cost is not. My main point is even marginal cost is zero, there is

Sorry for confusion, second marginal was mistake, I meant even marginal cost is zero, actual cost is not. My main point is even marginal cost is zero, there is another cost ignored (saas service example) If you are ok with to pay 0 when marginal cost is 0, you should be ok to pay X when marginal cost is X. Then this justifies for you to pay marginal cost only. So if we move to physical world, I can say I paid for one iPhone, but if marginal cost of iPhone is half price, so If I bought one, I can steal one.