I completely agree that we can't know how it will turn out in the long term (but why not try it and scrape it if it doesn't?), but the idea is that individuals could use the income to retrain when forced out of work, and to be able to provide an environment for their kids that give their them at least a chance at upwards mobility.
Again, I don't think it will lead to perfect equality. Nor is it a magic bullet: one pet-peeve is that everyone seems to be concerned with income, but less so with wealth per-se. Some people have proposed a tax on land itself but not improvements to land: I am not trained in economics so I can't speak to its efficacy (perhaps it's an outmoded idea today), but from a moral standpoint such a tax (with perhaps a "homestead exemption" for one's primary residence up to a certain value) seems a lot more fair than an income or property tax (which also taxes improvements to property that benefit the community).