The BBC has some background on the practice.

the issue really serves to highlight the necessity of governmental oversight of religious practice. Not to define what religious practices are “correct” or not, but rather to simply be blind to religion when evaluating issues against the law. The question of whether self-flagellation is an authentic Islamic or Shi’a practice is a (bloody) red herring - the question is simply whether the actions violated Law. And they did, so Mr. Zaidi needs to be prosecuted accordingly. Bringing this issue into the domain of religious freedom only serves to cloud the issue, and taint the entire muslim community, Sunni and Shi’a alike.

good discussion at Deenport, also, particularly this comment:

apart from the (elected) government, who else can provide public safeguards when religious practices veer into problematic areas, for instance where they are forced upon those who are uncomfortable with them, or simply don’t accept them as ‘correct’ religious practices?

I do believe that ultimately, these safeguards protect religious minorities even while they impose limits on public manifestations of religion. Do we need protecting from ourselves? I think that sometimes we do…