6' is nowhere near enough distance to be safe indoors in a room with potentially up to hundreds of other people in it. The virus can stay airborne for hours in enclosed indoor spaces.

If you have a lecture hall of 100 people that meets regularly each week, and the people in it aren't wearing good masks, it's practically a guarantee that by the end of the semester everyone there will have gotten it.

Yep. Don't forget about air conditioning, as well as shared facilities such as restrooms, break rooms, cafeterias, and so on.

And don't forget _bad_ air conditioning / poor ventilation in old buildings, with which universities are replete.

The 6' rule isn't a magic bubble of impenetrability. It's just a rule of thumb that (1) most people can easily interpret and enforce and (2) is expected to reduce the rate of spread "enough" to make it worth enforcing.

Likewise masks don't make you safe, they make you safer, etc...