disable speaker by default or optional for better security?

Agreed. Whonix takes some learning though, for sure, especially if both Whonix and the virtualizer are new to the user.
End of the day users stay with defaults. The peculiarities in Whonix (no sound by default for example) are well worth some more support tickets if the tradeoff is lower security. Sure, we can instruct users to turn it off themselves / use headphones etc. But if the users read that there’d be no problem in the first place.

Created:
http://forums.dds6qkxpwdeubwucdiaord2xgbbeyds25rbsgr73tbfpqpt4a6vjwsyd.onion/t/change-virtualbox-vm-shutdown-default-option/7309