[dragonwriter]

> What stops the Google's of the world from simply ignoring every dmca takedown request?

The same thing that leads them to make deals with big money copyright-based industries for copyright systems that go far beyond what the DMCA safe harbor requires for situations it covers: the fact that they are deeply and actually aware of the copyright violation they facilitate (putting them outside of the DMCA safe harbor to start with), and rely almost entirely on the fact that that is hard and expensive to prove (which the DMCA negates, but which forces them to go beyond the DMCA for industries for which the cost and expense of proving actual knowledge would otherwise be worthwhile.)