This is a fairly big question. On some levels, I think that a question like this strikes deep at the heart of all learning and goes to the very core of what teachers do and how students should progress. I don't think that there is an easy answer to this particular question. More context is needed, certain situations will dictate certain results, and other platitudes that embrace deeper analysis will all be evident here. On one hand, I think that there is something intrinsically valuable from the errors students make and that moment of self- realization that comes out of it. Sometimes, it is that proverbial light bulb that really jars a student into reality, enabling them to embrace in a more full element the path of doing right, being right, and existing in a sphere of comfort in both. This is something that is forged out of the painful fires of errors and mistakes. Naturally, these mistakes are seen in the academic realm, such as students understanding the need to embrace successful academic habits or refraining from academically destructive behavior. I don't think that this analysis exists in the realm of actions that endanger other students or threaten to subvert a healthy school climate.
The flip side to this is that there are so much attached in the modern educational setting to standards based educational reform. These arenas, along with "high stakes" standardized testing, makes student mistakes so painful for so many. There is little in way of learning curve, little time in terms to facilitate this learning process, that serious mistakes carries with it significant challenges for students, adults, and stakeholders in the learning process. I think that this is where "outcomes- based education" is not entirely compatible with the notion of making mistakes and embracing the process- based learning that is a part of it. In this, the challenge in the question lies.