I don't know how to break this to you, but surely you know there is already a grossly impoverished group of people working 6 days a week for $3.25 an hour without UBI.
If you add the UBI to their income they'll be hugely better off and they might even be able to choose between working those 6 days or staying at home and looking after their children, or caring for an elderly relative without the risk of being made homeless, or being unable to afford food for their family.
Maybe, maybe not.
For clarity, I am a fan of UBI. But I'd like to run through a hypothesis about an adverse effect.
If you add the UBI and costs go up accordingly, the real, marginal benefit they can obtain by working for $3.25 an hour will actually decrease.
This means someone who is in circumstances where they can currently earn a meagre income to tip the balance to being able to make ends meet in that circumstance, will find their ability to work the same amount in a UBI world will not tip the balance to being able to make ends meet.
In other words they will be pushed to change circumstance, towards more work and/or lower cost. E.g. move somewhere cheaper, work more hours.
This does not sound like a net benefit for the already impoverished. It sounds like a trap, because low-wage working will provide less marginal benefit to change what people can afford when they are stuck.
If someone is making ends meet by working at your (illegally low) wage, then having that wage _plus_ UBI means that they are UBI rate / existing wage times better off.
The wage's percentage of total income dropping is a red herring.
No one will be pushed to work more when they have _more_ resources at hand.
That's why I wrote "real", as in adjusted for inflation.
If you want to help poor people, start with radically capping and reducing rents per m^2 everywhere. And by "radically" I mean radically, not just halving them. That's one of the biggest problems in almost every country and it will get worse and worse if current trends continue.
US population is what, 300 million, ~75% of that are adults, multiplied by something like $35,000 is what, 8 trillion? The top 1% have a wealth of 35 trillion, US GDP is around 24 trillion - is it acceptable to spend 1/3rd of your GDP on eradicating poverty and creating a more equal society?
I just wanted to make clear that it's possible to implement UBI. There are many reasons against UBI, but not the ones you gave.
Personally, I'm against UBI for two reasons. First, it does not solve the fundamental problem, which is capital accumulation an ever increasing gap between the rich and the poor. The more money you have, the more money flows to you, and the gap has grown insane. Unless this trend is addressed and reversed, even UBI cannot prevent massive social unrest in the long run. Second, UBI makes it mentally and morally easier for employers to fire people and to lower wages even further. In the end, it will lead to a grossly impoverished class of UBI recipients who will work 6 days a week for $3.25 an hour to supplement their meagre UBI.
In my opinion a classical welfare state, maybe with a negative income tax, strong worker protections, tax-funded education and health care, and strong means to prevent wealth accumulation are the only ways to tackle the problem in the long run. Reforming hereditary laws and stopping almost all "financial products" would be a good start. Right now, once you have reached a certain threshold you can just live off by speculating on Wall Street and juggling around virtual money without ever producing anything of (non-monetary) value. That shouldn't be possible at all.
A deeper problem is that the whole model of existing economy is flawed, because it's based on permanent expansion, which leads to fast exhaustion of natural resources. It is simply not maintainable on Earth for more than 200 years from now.