Work ethic might be engrained into our culture, but someone who is brought up in a society where UBI is normal and they are just a few years away from becoming "rich", I think not-working-ever is a very enticing idea and many teens will fall into that trap.
#2 Switzerland has a very high cost of living so I'm not sure 2,300 Swiss Francs is that high.
#3 Your second paragraph is 100% begging the question. I'm open to the idea that UBI might be good or bad for work ethic but there simply is not enough data for you to have the confidence you do in your conclusion.
Trying to figure out how this would work. Presumably a bank would only lend a portion of the UBI to you
Therefore, the loan would have to be dismissable in bankruptcy. So a UBI loan basically reduces down to nothing more than an unsecured "personal loan", which is something you can get today, albeit at very high interest rates:
https://www.nerdwallet.com/personal-loans?annualIncomeFilter...
Also with UBI you are guaranteed a certain amount of income for the duration of your life. You can go to a bank and take a loan against your UBI. A big portion of the UBI will end up at the banks because basically the loans are guaranteed by the government.