Direct democracies are virtually nonexistent at the national level; Switzerland, which is still a mostly-representative democracy, is probably the closest thing there is.
> Introduction beforehand sows the seed for a direct transfer of wealth from the 49% haves to the 51% have-nots.
Means-tested welfare plus taxation, which most countries have, does that, too; I don't see how UBI is any more dangerous in that regard, nor do I see the runaway spiral of voting unsustainable benefits anywhere, despite the popular meme that this is the natural consequence of democratic control of the public purse. So, before I take this particular slippery slope argument seriously, I'm going to need to see some convincing argument of how UBI is different in some relevant way.