I am in favor of doing with Mars as we wish. When Western Civilization had "first contact" with various "alien"[1] native societies around the world, most of the impact flowed from civilization to the "aliens". Civilization continued on and most of the alien societies became footnotes in history. Might makes right, and unless the Martian bacteria are crafting starships in their caves, I think we should take samples for scientific study and then open Mars to homesteaders. The Martian lifeforms have had just as long to do something productive with Mars as we have had with Earth. It is not our fault if they are still just bacteria.

[1] Meaning literally foreign.