Implementation is the key. There's so many 'red flags' with big consequences that it is very risky policy to implement in any large nation.
1. Would able bodied people keep working? I think it is nice for academics and others who have jobs they like to imagine they'd keep doing them. How about being a miner to dig for lithium? Even if you do keep working, will you do the part of the job you hate knowing you could always just say screw it and get on the UBI? Yes, maybe companies make work more pleasant and can keep people working efficiently, but the what-if it doesn't is always there.
2. Would you be able to compete? Unless the UBI is done on a global basis, it introduces some tricky timings. Maybe you lose economic competitiveness? Maybe your country gets flooded by immigration for the free money? Do you start to have stricter border controls? Does anything in it impact free trade rules.
3. Savings are theoretical. There's always talk of replacing all large parts of our social programs with UBI. I don't buy that. I'm in Canada. Just getting a wage freeze for public sector workers is hard enough. Can you imagine a government which says I'm going to lay off a million public sector workers (or whatever the number is). Yeah, good luck with that.
4. The UBI is theoretically capable of giving you an okay life. For simplicity, a single person gets a one bedroom apartment, cable, cell phone, food, clothes.. Will we set the bar high enough for that. Reality is we already have free money in most western countries. It's called welfare. It's just set so low and the process so arduous that most people don't want to be on it. Do we risk that happening long term and just having UBI end up as welfare.
5. What will people do with boredom. Yes, some percentage will pursue interests. But will people feel useless, unproductive...? Some people want something to do and work has provided that for thousands of years. Be it farming, cleaning, factory, technical, social... whatever.
I have nothing morally against a UBI. I just think it's really premature to be talking about it as a serious policy. There's just so much work that needs to be done right now.
I'd much rather see a focus on making jobs more pleasant and even guaranteeing / subsidizing jobs. Heck, we could use several more people on my team at work right now. Don't have the budget for it of course. But eh, if we're going down this road of UBI, why not have the government pay for a few folks to help out.