The accepted answer on How can large open source projects be monetized? mentions open source SaaS.
Once you are successful enough in one of the above, you can afford giving away your software for free (as in free beer).
So how can a startup whos core product is SaaS safely grow until youre "successful enough" if you are Open Source? Couldnt someone with bad morales and good timing fork our minimum viable product and own us by simply running a better launch campaign?