Plato's philosophical mentor/literary protagonist Socrates (we know of him mainly through Plato's dialogues) spends his hours and days taking every man's ideas to task, asking each to examine his (sadly, no "her") beliefs through the technique of dialectic—examining statements by subjecting them to all manner of contradictory propositions to see if they hold up. The idea is inherently familiar to us, as, not coincidentally, it is the foundation of our legal trials in most of the West. It bears note that the same process is used whether we start from the assumption of innocence or guilt.
So why is the concept of deliberation to arrive at the truth problematic? Because philosophical deliberation, which, on some level, is meant to be a tool to arrive at ethical decisions in the practical world of events and consequences, can also serve as a paralyzing force that problematizes every course of action until it seems of specious application to actual situations. Put more plainly, we just don't have the time in the complex world of human affairs to seek philosophically untroubling solutions to the constant demand for ethical action in the world; the world doesn't stop to wait for us to make up our minds on ethical questions requiring prompt (and critical) decisions.
Nowhere is this more apparent than in the world of bioethics: whether we speak of abortion, euthanasia, assisted suicide, stem-cell research, human cloning, "conscientious objection" to vaccination, blood transfusion, hospital care, what have you—we face situations in which the lives and life qualities of countless humans are contingent upon the construction and implementation of actual policies; the kind of policies that have legal, economic, and other material considerations that simply do not wait for philosophical consensus. Nor, really, should we desire that they do: anyone who believes that consensus need always precede policy would have to live in a world in which each new technology were innocent until proven guilty, in which we gave a long enough ethical rope to each technology to morally hang itself.
I am reminded of a law school joke (it isn’t the funny kind): three judges go duck hunting and see a duck fly overhead. The Supreme Court justice begins to lecture on the jurisprudence of biodiversity and the rights in principal of ducks; the circuit court justice considers the ethics of hunting and the appropriate use of firearms; the third, a district court judge, levels his rifle and takes a shot at the duck. Ultimately, all of us are all three of these judges; we must have theories and theories of theories, but, unless we plan to retire to lives of ascetic contemplation, we all must make practical and hard decisions in the world—we all have to shoot at the duck.