Which cursor-related warnings should be errors?

The developers are currently discussing changing several cursor-related
warnings to hard errors. If PostgreSQL were to be designed from scratch,
there would hardly be discussion about this, but now we are wondering
whether any existing users would seriously be affected by this change.
The cases under consideration are:

Fetching from a non-existent cursor:

peter=# FETCH ALL FROM non_existent;
WARNING: portal "non_existent" does not exist
FETCH 0

Closing a non-existent cursor:

peter=# CLOSE non_existent;
WARNING: portal "non_existent" does not exist
CLOSE CURSOR

Declaring a new cursor that uses a name already in use:

peter=# BEGIN;
BEGIN
peter=# DECLARE foo CURSOR FOR SELECT 1;
DECLARE CURSOR
peter=# DECLARE foo CURSOR FOR SELECT 2;
WARNING: Closing pre-existing portal "foo"
DECLARE CURSOR

So if anyone can come up with a reason that theses WARNING: messages
should not be changed to errors, please speak up.

--
Peter Eisentraut peter_e(at)gmx(dot)net