When you just have one guy cloning himself with government subsidy, there are totally different dynamics at play.
The system of UBI changes the incentives to create this behavior. I am not even saying it is rat-like; In my previous comment I discussed the differences between our world and the rat utopia. In the rat utopia, reproduction is still limited by the interplay of sexes and you eventually get failure of the system through a breakdown of reproduction. It would be more accurate to describe the most successful strategy under UBI as "tumor-like", where the failure mode is based on a strain in resources.
The richest, safest societies don't have infinite welfare because they have cemented a culture which rejects welfare, and reproduction is currently limited by either culture (women's expectations of their partners) OR resources (look at https://www.msn.com/en-us/news/world/the-chinese-billionaire... or what elon is doing). What happens when reproduction is limited by neither? We already see the effects of this in say, Africa where you have a massive population explosion caused by aid.