Oh, no, I don't mean to be certain! Which is why I put that disclaimer about this being one possible line of thought at the very beginning. This is a blog post, after all. :) But, yes, abiogenesis is likely to be relatively common given the vastness of the universe.
Of course, I love Ringworld! Read a few more of the Known Space series as well. Haven't read them in a decade or so though! Probably a good time to revisit. :)