Yeah, if "universal income" is on the table, it needs to be without qualification. None of this waffling about when it comes to "How much is enough work?" or "Is it right to be supporting criminals?" There is no answer to those questions that will satisfy a majority of people. Keep it to pragmatism - will it make society work more smoothly as a whole?
If you really want to focus on particular groups, then you need to frame your questions in terms of who benefits, not who's punished. Really, your question shouldn't be, "How will we punish the leeches?" Your question should be, "How will we reward the creators?" The premise of a post-scarcity society is that letting people "leech off society" ceases to inconvenience the people who don't. When there's no cost to the members of society you prefer, why on earth should you even care about the hypothetical moochers? What justice is there in punishing people for living the lives they want to live, when there's no meaningful cost to anybody else?
The rewards to the creators are obvious - prestige, extra wealth (to whatever extent that's meaningful), and, most importantly, a sense of purpose and accomplishment. To whatever extent anybody ever accomplishes anything great, those are powerful motivators - much moreso than a minimum wage ever has been. Here's how a properly-done post-scarcity society would differ from current Western society, in terms of awesome people doing awesome things:
- The people who already have the ability, resources, motivation, and luck to do great things will continue to do so.
- People who lack resources and luck will find those are less of a problem - you'll see more wonderful things from people who could achieve but were held back by the system. I expect this is a majority of people, but it's certainly nonzero and a clear gain over the present.
- People who are content to coast through life will still be able to do so, but instead of working in fast food or as low-level office drones, they'll be free to do so from their couch. Nothing of value has been lost.
Who, exactly, loses here?