Well, it's true that humans are easily injured, but they also easily heal, compared to robots which need a repair shop. The problem about oxygen could be solved by genetically engineering a human to coexist with algae under their skin.

This would also produce cool skin colors! But anyway, the reason I'd build myself as a robot is not for those benefits, but because I could add parts whenever I wanted

Or customize, rebuild, reconfigure, etc. Nice, no?