I do not have an indoor voice. I am not ashamed of this (my mother is but that is not my problem). I grew up in a big, loud, talkative family and if you don't make yourself heard you won't be. This has given me the confidence to be vocal socially, academically and definitely helped in sports!
I do however agree that there are certain conversational topics which would be better discussed at lower volume but my control over my vocal chords (much like my control over the thoughts I let loose) is a little limited so I have to make the effort to take these convos somewhere private!
While I can see the merit of 'the indoor voice' I think many a person's indoor voice becomes their only voice, then becomes their inner voice.
I like quiet people (I also enjoy the company of loud people) but I always worry about them being left out or left behind because they don't put themselves out there like us loud folks. There's nothing wrong with being softly spoken or with being selective about what you choose to share with people I just think too many quiet people let themselves become introverted when in the presence of unfamiliar people or loudies.
While there will always be the odd people who can't handle my noise levels, or to whom I might appear a little brash I will always be proud of my voice because I'd rather make noise than become invisible. I agree that silence can be golden but it's very hard to hold a conversation with a mute.