The second question is a common question of UBI. Wages still work the same way, and like a minimum wage, a UBI would put upward pressure on all wages. You'd get somebody to do any of those jobs provided the additional income was worth it. Just like now; if the price is right, most people will do anything. Except instead of the baseline being nothing but the breadline, the baseline is some financial threshhold. Obviously its effects are dependent on the size of the UBI, which could be anywhere from supplemental to whatever. The first question is a bit more nuanced, but I'll defend my position best as I can. As far as what "pursuing their passion" is, I'd generalize it away from such hyperbole to a simpler idea of "doing what they want." More freedom from the limitations of circumstance. We often associate "pursuing a passion" with meeting a threshhold of freedom. Saving enough money to quit, saving enough money to go to grad school, uni, or college, or trade school, or taking time off, or starting your own business, getting the house. To the extent that we consider "pursuing a passion" a matter of "meeting a personal threshold or goal," I'd consider welfare helps people achieve their goal of "survive long enough to find stability." I will also ask: does getting a raise make you lazy?
If there weren't a "suck-tit at the expense of other citizens" option which allowed them to "not work", they'd take those undesirable jobs out of necessity... at least until they got the notion, "I don't like this. I want better for myself". And then they would do what they could to make things better for themselves. (Didn't they try that back in Old America?)
UBI would cause massive inflation. It would shrink the labor pool which would mean employers have to pay more to get help which means they would have to increase prices which means you'd have to increase UBI and the cycle continues.
Whether it would cause inflation depends on implementation and circumstance. The pool of money is still the same, it is essentially redistribution, so no direct inflation. Companies would also get more customers because everybody has more money. To say which way the balance would swing is not clearcut. Also, if fewer and fewer people have jobs, nobody has money to spend on the companies. The same argument is made for minimum wage, isn't it? You're gonna shrink the labor pool and make everyone raise prices. But studies have shown raising the minimum wage doesn't affect the labor pool in proportion to its positives.
It is true that to talk about "pursueing one's passion" is most often associated with musicians, artists, etc. Why aren't welfare recipients into arts , or sports, or any "valuable" professional hobby? may be their basic education missed something important: getting them to develop a vocation. Ah effectively : who would do the crappy jobs? Usually, the education system was designed to educate from a young age te "chosen" children who only qualify for the jobs noboy wanted to do. Then some leftists did not like that, so now illegals are the one normally taking up these jobs. Can't the engineers design robots to clean these places, and can't these places be designed so that the robots can do the job ?
We will always be relevant to ourselves. In an ideal world, automation is something to be welcomed by Homo sapiens. If we can free ourselves of the druggery of mindless labor through automation then we should celebrate. But have we evolved as a species enough to take full advantage of our new freedom. Now that we don't have to vacuum the carpets, walk the dog, or gut chickens all day long, shouldn't we have more time for those endeavors in which the human brain is an essential component, such as the arts --music, theater and visual--, abstract mathematics, architecture, the sciences, and the humanities. But will we instead use our new freedom to catch up on past episodes of "Judge Judy" or "Lock-Up?" Can there be any doubt that Marx was right to proclaim, "capital drives out labor." Now that we see that it does, we homo sapiens will need a new paradigm for living. That's coming! It is only a revolution or two away.