I used to think the same thing, but then I met my husband who rides, and now I do too. The way he explained it to me is that you need people to hear you, they may not always see you, you at least get a second chance to not get ran over if they can hear you.
There are few things I hate more than unnecessarily loud bikes. I could care less what the justification might be. Most people hate this shit, and nobody is impressed.