Why would it be bad?
Do you really think that the entire world will convert to your pet open source application because you have an aversion to commercial software packages.
Effectively it's your attitude that's hurting open source far more than any support for interaction with non-open applications ever will.
Without POI (or similar projects) people who want their applications to interact with MS Office will be forced to use commercial APIs which will prevent them from releasing their application into open source themselves (if they have that inclination).
As a programmer you cannot choose (usually) the platforms to be supported. Your customer or employer has a software platform and that's the one you're going to have to write for.
You might be able to bully the local butchershop into switching to OpenOffice for its 2 workstations, but I doubt that attitude will get you anywhere (except kicked out of the building) with a multinational.
Like it or not, MS Office is the de-facto standard to which all office applications are measured and which all have to support.
Maybe if OpenOffice were really as great as you consider it, it might be able to change that but to do so it will have to support reading AND writing MS Office files because the customers and other contacts of the people and companies you need to get to use OpenOffice will still be using that (plus the users will have a considerable existing document base all in MS Office format that they will require to be able to read and edit in whatever new office platform they may choose).
And don't forget to make certain the retraining of users from MS Office is minimal. No more than a few hours to get started or a few days at most to get anyone to the same level of expertise (s)he has now in MS Office or no large corporation will accept it for the simple reason that the transition will be far too expensive for them (even with the license costs of MS Office).
So yes, there is definitely a need to read and write Office documents from open source software.