We can't go on relying on these glass and steel butterflies to explore Mars for us. Like many objects of beauty and elegance, they're physically fragile, as easily broken as icicles. That's not good enough for a world we hope to someday make our second home. Mars needs people. Humans can adopt new ideas, adapt procedures and improve the chances of problems and emergencies being overcome.
Humans can react.
Probes, no matter how much we try to convince ourselves otherwise, can't. But perhaps most importantly of all, humans can experience things. We can be moved by what we see, hear and feel. We appreciate beauty. Probes only take the photos they're ordered to take.