Of course it is all conjecture but I tend to go with the "zoo."
We are an as yet primitive and fledgling space faring species still segmented like animals in cages by our inability to agree on what being an earthling actually means (read political and religious differences).
It seems logical that the "prime directive" is a universal idea.
After all, would we ourselves go to another planet and play "gods" to whatever "lesser" life might exist?
I think not, but who can say?
But there is even some evidence (though there are surely arguments against it!) for the zoo hypothesis.
It comes from an astronomer, Bernard Haisch of ufoskeptic.org:
"Recently astrophysicist Ken Olum at Tufts University argued (gr-qc/0303070) that anthropic reasoning applied to inflation theory predicts that we should find ourselves part of a large, galaxy-sized civilization, implying that the "We are alone" solution to Fermi's paradox is inconsistent with our best current theory of cosmology. Beatriz Gato-Rivera, a physicist at the Instituto de Matematicas y Fisica in Madrid, followed up on this (physics/0308078) with the hypothesis that Olum is correct, but that by design we would be kept unaware of a greatly advanced surrounding civilization. She also argues that modern superstring and M-brane theory further aggravate Fermi's "missing alien" problem. It is quite strange that while our best modern physics and astrophysics theories thus predict that we should be experiencing extraterrestrial visitation, any possible evidence of such in the form of a subset of UFO reports is ignored or ridiculed."
The ETH and its long history on this planet and a possible explanation to such a profound question supported by our very own physics theories!
Where the telescope ends, the microscope begins. Which of the two has the greater view?