There are probably as many reasons to write virii as there are psychotics who can program. The question is not why they do it, but how we can stop them. The prospects of prison doesn't stop them because no one commits a crime with the intention of being caught. Prison is a good place for them but you have to catch them first, which means they have caused problems.

We can make it more difficult for them. We can keep our systems up to date. We can work with security personell while developing system specifications and have them test our systems after being written. There are a myriad of details we can work on to keep our systems safe and funcitoning BUT we don't. It costs too much or it takes too much time.

We are part of the problem because we have given them the opportunity to distribute the malware. Perhaps if we were more vigilant there would be less damage.