Sending human beings to explore Mars poses a high risk of biological contamination that would prevent accurate identification of alien life.

“My fear, or anxiety, or taxpayer arms akimbotic-ness is, if you send people, you're going to contaminate it. You're going to make a mess. And then, will you be able to determine, distinguish between what may have grown the leopard spot patterns or what humans brought by accident?”

Sending humans to space does not make missions faster or cheaper and creates significant contamination risks for planetary science.

“Plus, more to the point, at no point in history ever has adding humans to a space mission made it cheaper or happened faster.”