My primary concern with UBI is not the concept itself, but the risk for people in power to use it against the people. Once UBI exists, people will rely on it for survival. It will be the single most influential campaign topic. Worse, if UBI were to get 'Obamacared' then we'd end up with a massive battle over implementation, followed by a much worse system than the one we had prior (worst of all worlds with numerous '…
M4A is similar as well. I guess all big social safety nets have this problem. UBI and M4A would encourage me (and others) to pursue less lucrative pursuits (arts, research, gamedev, entrepreneurship, etc) but it would be hard for me to quit my nice tech job salary if there's the specter of the GOP potentially killing the benefits that enable my pursuit. And that doesn't even compare to the effect that uncertainty has…
Not to mention you lose the overhead of dealing with insurance, for you and your family.
But yeah, I could see a class of people who would use UBI to permanently slack off whereas they would be highly productive otherwise.
Edit: Note I'm from Canada and have taken healthcare for granted until I went to the US. My experience has been overwhelming positive with universal healthcare, and the only complaint is I've had to wait a few hours per emergency visit. Zero wait when serious though.