Normally for RPGM games I can disable sound through the interface f the game--unless the developer has specifically overridden that option. Additionally, I use my computer for more than playing these games. Yes, I can just turn off the sound through the mixer, but I shouldn't have to do that just to play a stupid game.
I get incensed about this for a number of reasons. First of all, I would rather listen to music of my own choice when I'm playing these games, as the choices of others don't always match my tastes. Secondly, my current situation gives me very little privacy--enough privacy that no one is looking over my shoulder when I'm playing, but I don't want to attract attention. Thirdly I just think it's really, really rude, and choose not to support developers who do so. Also, to be perfectly frank, I've yet to encounter a game that's unplayable without sound effects and music.
I know there are many who enjoy music embedded in their games, but there are also plenty of people who don't. That;s why the controls exist to disable sound if the user chooses to do so.