So-called “urban renewal” programs provide some compensation for the properties they take, but no compensation is possible for the subjective value of these lands to the individuals displaced and the indignity inflicted by uprooting them from their homes…. [E]xtending the concept of public purpose to encompass any economically beneficial goal guarantees that these losses will fall disproportionately on poor communities. Those communities are not only systematically less likely to put their lands to the highest and best social use, but are also the least politically powerful. If ever there were justification for intrusive judicial review of constitutional provisions that protect “discrete and insular minorities,” surely that principle would apply with great force to the powerless groups and individuals the Public Use Clause protects.