All my friends know that I'm a huge fan of Universal Basic Income for a variety of reasons. I'll outline here a collection of my main arguments for UBI.
First things first, I'll define UBI: it has to be Universal, it has to be Basic, and it has to be an Income.
Universal means that everyone (this can be reasonably restricted to every adult citizen of the country one is talking about implementing UBI in) must get it, regardless of employment situation. This is a very critical part: if you get a minimum wage job, you still get the UBI on top, so that it doesn't disincentivize work. It can make work less incentivized than before, but it can't disincentivize it the way many welfare programs work and create poverty traps.
Basic means that it must be at least enough to reasonably live, whatever that number is. If you think someone needs 1500$/mo to live, then it must be at least that. However, there is a caveat here: I don't think it's unreasonable to expect people on UBI to make more reasonable living decisions, notably such as living somewhere cheaper than they'd like.
Income means that it must be money, not coupons or food stamps or whatever. This is a crucial part, and is the part I consider most important to weird people and marginized groups: the less the Standard Majority Needs correspond to your needs, the less you'll get value out of being provided those; with money, instead, you're free to decide what it is you need and value.
Here are some of my favorite UBI arguments:
The Housing Crisis: with UBI, people don't need to work in those giant, super-expensive cities anymore, because they don't need the jobs that are in them. UBI not only lifts a ton of people out of poverty and helps the homeless tremendously, but also lets people move out of the giant cities, thereby decreasing demand and possible making rents in those cities actually go down as a result. In addition, if UBI is a reasonable amount, it's not out of the question that people could purchase their own homes with loans paid with UBI; banks will love giving loans to people with an income that is guaranteed to remain forever, and eventually this could emancipate a lot of people out of depending on landlords.
Healthcare: notably in the US, there are reasonable arguments to be made against either a public healthcare system or a private healthcare market. With UBI, we can get the best of both worlds: make the healthcare private market, but make everyone's UBI be enough to cover, on top of other living, a reasonable private health insurance. That way, those who want to opt out can do so, insurances and health companies are still incentivized to reduce prices to an extent (or more people might just use that money on something else), but everyone is guaranteed to be able to afford healthcare.
Discrimination: a large part of the cycle of racism (poverty → lesser education → lesser jobs → kids themselves in poverty) is the employment part. UBI not just helps by being redistributive, but also by making it okay to actually not have a job, and greatly easing the pressure poor people having with paying bills or food. If coupled with the housing crisis solution above, this could even lead to entire new integrated communities largely thriving on UBI.
Government corruption and lobbyism: if they have the UBI to afford it, the poor and middle class could participate a lot more in funding political parties and maybe even lobbyists; in that sense, UBI has the potential to realign even democracy with the interests of the people.
Domestic abuse, etc: all sorts of situations of this type where one party is dependent on another for money, are suddenly alleviated if both parties get free money enough to live.
Exploitation/poor work conditions/poor wages: UBI gives workers the ability to just refuse employment altogether, giving them tremendous negotiating ability in the labor market. Raising the price of labor would also accelerate automation, which we should want (and which, if we have UBI, is actually fine).
Even Conservatives!: with UBI, lifestyles such as the traditional nuclear family become easier to actually implement, as the wife can contribute to the family finances with her own UBI.
Not Enough Enterpreneurship: a lot more people would be able to start working on projects that might actually create value, and work on those with other people, if none of them needs an external source of funding. This also covers usually less profitable prosects, like artistic careers.
Welfare But Better: usual welfare systems are extremely inefficient and bureaucratically heavy. On the other hand, just giving everyone a fixed pile of money is extremely simple and easily implemented; with the same funding, a UBI scheme could thus result in actually a lot more money actually going to the general poor population.
UBI is not that far away politically: UBI is already a fairly popular idea in the field of economics (and even in the rationalist community). Really, all we need right now to get UBI implemented is popular support, i.e. you reading this right now, being in favor of it.
But, really, these are all somehow related to the least practical but, in my opinion, most important argument:
Edit 2021-02-24: Another, more complete list of argument can be found here.