Given the implications of time dilation on the crew of the Endurance mission, why send people at all? TARS and CASE seem more than capable of operating the ships themselves and wouldn't care about how much time was passing for each other or back on Earth. Whoever they chose to rescue could have started Plan B without risking any more crew.
According to the original script, the problem is that robots simply aren't reliable. Placing the survival of the entire human race into their hands is both unnecessarily risky (in the sense that they could malfunction) and unnecessarily risk-averse when they're already willing to treat their finest minds as expendable units:
COOPER: You’re taking a risk using ex-military for security. They’re old, their control units are unpredictable ...
WOMAN: Well, that’s what the government could spare.
It should be noted that TARS and CASE apparently performed well above expectation.