These are damaging. Anything that can be stored on a computer can be sent via an email attachment. Just as you wouldn't run a mysterious program some stranger gave to you on a disk, you shouldn't run some program that some stranger sends to you by email. The same general cleanliness practices apply. But reading the plain text of a mail message could never be a danger.
Some attachments can contain subtle viruses.
It is possible, for example, to create a virus using MS-Word macros, so that when the Word program is run on the file the virus will actually be executed. Basically, a Word file can contain a program that gets run when Word processes the file. Again, this is no more true of Word files sent by Email as by floppy or by any other means. Also, the Standard PC desktop at Cranfield runs virus checking software that can catch the known Word viruses. However, there is no indication that there these hoaxes are genuine warnings about such viruses.