Why are software patents wrong?

[threeseas]

Two catagories of answers:

symptoms and cause

or from the other direction:

cause and effect.

Seems to me many have found arguement against software patents that only 
deal with the symptoms or effect of software patents, rather then the 
more fundamental underlying reasons why software doesn't qualify for 
patent status.

So how about it?

why do you think software should not be patentable? and is your answer 
cause or effect?