The budget and general public interest will be 1000x greater if humans are sent.
“Robots explore Mars” is a daily news highlight.
“First humans land on Mars” is a global historical event.
General public interest will vanish once people realize that the journey will last two years and likely start 30 years from now. Oh, and they won't see the event live anywways.
The trip to the Moon was a free trip to Jurassic Park in comparison.