"It may be considered as an objection inherent in the principle, that as every appeal to the people would carry an implication of some defect in the government, frequent appeals would in great measure deprive the government of that veneration which time bestows on every thing, and without which perhaps the wisest and freest governments would not possess the requisite stability . . . a constitutional road to the decision of the people ought to be marked out and kept open, for certain great and extraordinary occasions"