>If I would need to choose only between UBI and high taxes on the rich I would choose the latter
There no need to be exclusive, and actually having concentration of wealth in a few hands is already a social construct. A society can also thrive without high income disparities. Taxing the rich is just taxing on what was captured from the non-rich.
It is about the practicality of convincing people to do something. Many people I know are inert and would say no to change. Even those that want change have a favorite topic.
So, personally, when discussing economic topics I discuss the taxes part, which is so clearly unjust when explained (most countries tax less capital gains than work, which results in rich people able to accumulate things faster).
Additionally, I am not convinced that me or you know exactly what will work - humans are complex. So while I hope that it is possible to have "A society can also thrive without high income disparities.", proposing too many changes at once might result in an undesired result. There are enough examples in history where good intentions led to catastrophes.
>captured from the non-rich.
What do you mean by this? The economy is not zero sum, it is possible for everyone to get "wealthier", even if the spread increases.