MLK is largely seen as a virtuous, wise person. A lot of moral sentiment enters into people's opinions on social economics. Also, people look to group sentiment

MLK is largely seen as a virtuous, wise person. A lot of moral sentiment enters into people's opinions on social economics. Also, people look to group sentiment to calibrate whether a proposal is more extreme than they want to think of themselves/be thought of. MLK having expressed a favorable opinion about it makes UBI less susceptible to "that's evil, naive communism"-style attacks.