I think it's actually exactly the opposite. We don't have the ability to definitively detect or not detect life on Mars. So if we send a machine with the goal

I think it's actually exactly the opposite. We don't have the ability to definitively detect or not detect life on Mars. So if we send a machine with the goal of detecting life and it doesn't, well maybe it's there we just didn't detect it. So it's better to pretend that we can't actually detect while actually sending detectors.