Teacher Tenure?

In California Schwarzenegger is pushing proposition 74, which would make it easier for school administrators to fire bad teachers and would increase for teachers the probationary time for tenure to five years from two. Is it too much to think that no school teacher should have tenure? That teachers who are good at what they do should keep their jobs and that ones who aren't should lose theirs? I don't really know the numbers, but teachers often say that administrators would indiscriminately fire older teachers (who cost more) if there weren't tenure. That would be a travesty. However, I know (and probably everyone has a story) of poor teachers who were teaching when they shouldn't have been. Teachers who should have been fired long ago. Some of those teachers are the most vocal ones when defending tenure.