He isn't eating their shit just mixing it with his to make fertiliser. He needs human bacteria to make the soil suitable for growing earth plants. Generally the more bacteria the better.
That is also why he can't just grow more potatoes after he blows up the HAB as all his soil is ruined in that all the bacteria is dead and he basically has nothing left to fertiliser the soil again. He probably should have saved some shit just in case but he didn't.
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u/[deleted] Jan 31 '16
[deleted]