By visiting a YouTube video, I am giving YouTube my consent to play me a video, including any sound it might contain. I completely expect YouTube videos to play sound and am prepared for it, unlike websites such as this.
No, that this is a double standard people have. They gripe about any non-YouTube site playing audio, but say nothing when they click a bit.ly link that redirects to a YouTube video page.
It doesn't. Flashblock is one of the most popular Firefox extensions[1], and variants are available in other browsers. Even though it offers some protection against hidden Flash elements and supercookies, it would still be popular just to prevent autoplaying flash presentations.
The author of Flashblock even specifically mentions YouTube on the extension page[2]:
Youtube videos not blocked: This is because they are now increasingly HTML5 Videos. I plan to add HTML5 blocking in the next version. Meanwhile you can try out a experimental version at:
http://flashblock.mozdev.org/installation1.html#unstable
This indicates there is a demand for the autoplay blocking feature alone, regardless of the medium.
Not that I care about unexpected noises in a situation like this, but I hope we all agree that unexpected and unwanted noises are genuinely annoying to many people.