No one's arguing that only a small percentage of people are geared toward pursuing high risk/high cost opportunities. But it's not really relevant to the idea of basic income or an indictment of the majority.
The vast majority are happiest when they are doing meaningful work, not by sitting on the couch and eating ice cream while being void of engaging work. This is true for people of all walks of life, the super bright, the super disciplined, the super motivated as well as the other end and everything in between. The concept of basic income would free people to pursue engaging work. Meaningful work does not have to come in the form of trying to cure diseases or build sky scrapers, or start a tech company.
Meaningful work is abundant and not limited by the arbitrary limitations created by a material-consumption-based society what was ushered in by the industrial age, which for the the majority has dictated what is economically viable to make a living. Meaningful work can come in the form of volunteering, gardening, looking after elders, helping the environment, creating beautiful neighbourhoods, social support, skilled crafts, the list is endless and not limited to people with above average intelligence or motivation. Right now these types of endeavours are not economically sustaining for people to focus on.
Given that technology will drastically cut down the amount of jobs required it is beyond obvious that the current orthodoxy just isn't applicable in tomorrow's world. It is obvious today and it's only get worse tomorrow. Autonomous cars and trucks alone will kill millions of jobs, how do these people find economically viable jobs? Office jobs will decline at an exponential pace, because there will be no economically viable reason to employ people for work that is done more efficiently by software.
Given that we can actually sustain billions of people's material needs with most of the work being done by our tools, rather than people, it is complete lunacy to handicap the population by limiting it because the majority won't actually be able to find economically viable work according to yesterday's economy. It is also completely arbitrary. The conditions have changed dramatically and the sooner we adjust the system to fit the new conditions, the better.