It doesn't, that I am aware of, any more than democracy allows unlimited incarceration without charges. Such things occur within any system, and any system is only as good as the people that run it.
That being said it makes me uneasy when people argue for a system in which people of different religions are treated differently under the law and one religion is made superior. That is a recipe for inequality and history backs up that that is the practice.
While many democracies, including and especially the USA, have a sordid history of practicing true equality, the system allows it and indeed strives for it. That is not the case with Sharia. Inequality is an inherent part of Sharia.