Was Tucker ethical to sell very risky investments to people who could not afford the risk? Would it have made a difference if they understood the risk they were taking? How does this relate to buying stock today?

I think Tucker believed in his ideas. He was not malicious in selling his investments. I think he was naive to think that the other car companies would not try to destroy his business. People who invested with him took their own risk considering how entrenched the big three automakers were in the American automotive industry.