I think it's one of my favourites this year if not THE fav. I think that the title "Without a Sound" refers not that much to a mute protagonist, but to the fact that in Korean (but not only) society many voices are unheard, many bad, criminal things happen without media and people being loud about those problems, because it's hard to handle, because of corruption, because it's an uncomfortable topic or because more powerful people make them keep quite...
Chang Bok said to Tae In "what will he do without him?", because people with impairments and disabilities, people from very poor families, orphans like himself really need more help, but instead are being mistreated and cast out like trash and in some cases really have no choice (if they don't want to starve). Not to mention mafia, human traffic for organs, prostitution, paedophilia... The movie may seem almost comic (I did laugh hard in many scenes), but it does make you think about some really heavy topics with many strong metaphors and question yourself what did YOU do about it, since you surely had more possibilities to make a change than the protagonist, a person without a voice (physically and metaphorically, although he did make many people "hear" him at the end of the movie). It also obviously blurs the line between good and evil, since the protagonists do some criminal things, but also some good things, so it's not them being evil in their nature, but some of their actions. It makes us question ourselves what’s right and wrong, what’s good and bad what do we think about a certain situation and if those beliefs depend on motives and circumstanced or if our moral is absolute.