 One objection to allowing a supplementary tier is that its existence might undermine the basic tier either economically or politically. It might attract better-quality providers away from the basic tier, or raise costs in the basic tier, reducing the ability of society to meet its social obligations. The supplementary tier might undermine political support for the basic tier, for example, by undercutting the social solidarity needed if people are to remain committed to protecting opportunity for all. These objections are serious, and where a supplementary tier undermines the basic tier in either way, economically or politically, priority must be given to protecting the basic tier. In principle, however, it seems possible to design a system in which the supplementary tier does not undermine the basic one. If that can be done, then a system that permits tiering avoids restricting liberty in ways that some find seriously objectionable.