There is no evidence that supports this idea that UBI makes people stop working. In fact, multiple studies have shown that very few people actually chose to stop working under a UBI, with the overwhelming majority of those people being either students who quit their jobs to focus on schooling and/or mothers who quit their jobs to focus on childcare. Even better, UBI allowed people the opportunity to leave their low-wage jobs in favor of higher-paying jobs/positions, since they were not as desperate relying on minimal wages to survive. The only real Leftist position against a UBI is that it doesn't go far enough, and is only a band-aid solution to the inherent problems of capitalism.