Critics of the voucher system note that, in some systems, it is possible to have choice between schools within the public school system without vouchers.
Furthermore, the choice exercised by parents within the voucher system often results in the selection of a religious school, so that public funds are given to a religious institution. Theoretically, a religious school which endorses extremism could be eligible to accept taxpayer funded vouchers. However, most legislation on vouchers would include a provision that public funds may only be spent on education, not other religious activities.
Many argue that given the limited budget for schools, a voucher system weakens public schools while at the same time not necessarily providing enough money for people to attend private schools. (The opponents assert a tendency of the costs of tuition to rise along with its demand, which would compound the problem.) Opponents also claim that the vouchers are tantamount to providing taxpayer-subsidized white flight from urban public schools, whose student bodies are predominantly non-white in most large cities. Proponents such as Milton Friedman respond that the poor have an incentive to support school choice, as their children attend substandard schools, and would thus benefit most from alternative schools. Consequently, minorities, especially blacks, would benefit and contribute to the diversity of private schooling. The rich on the other hand, already attend schools of remarkable quality in affluent suburbs and would have no incentive to switch schools. In short, the more decrepit the school one attends, the more incentive he has to switch schools and thus benefit from school vouchers.
Interestingly, some fundamentalist groups side with liberals in opposition to school vouchers, albeit on different grounds. The general fundamentalist opposition is based on the source of the vouchers, which would be the government. Fundamentalists (who strongly oppose any government oversight of their operations) state that, if a church-run school accepts a government voucher, they have thus allowed the government the "right" to dictate the school's operation and, by extension, the church's operation as well. Therefore, the government could order the church to stop speaking against practices such as abortion and homosexuality, since it now "controls" the church through its acceptance of government funds. Other liberals believe it is unconstitutional to provide government funding for church-run schools as it promotes the state sponsoring relegion.
Some generally support school vouchers only coupled with standard tests, they reason that if there are not standard tests the schools in the school voucher system will give more students passing grades or "lower their bars" in order to attract students.
Further more criticism comes from various rich and poor people, assuming their vouchers will actually meet their taxes. Poor people believe that their vouchers will be worth less to schools and so selectivity in private schools will tend to be more biased against them, rendering their children with increasingly detoriating classmates and hence a slower learning curve ending in below average performance.
Logic dictates that the government might try to face this problem making rich people's vouchers equal to poor people's voucher and hence making the already rich school systems -and arguably better performing- (ex:Beverly Hills Unified School District) vulnerable to reduced funding.