Why 4BSD 'stty' uses stdout instead of stdin

[ka at hou3c.UUCP]

> On 4BSD (and V7?) a tty must be opened for writing in order for a
> process to set the tty's modes.  This does make a certain amount of
> sense; if you don't want someone to write on your tty, then you usually
> don't want them to set your tty's mode either.

It certainly does not make sense to me.  Why would you give somebody
read permission on your tty but not write permission?
				Kenneth Almquist