Correct, it can cause lower employment rate as you mentioned, but that would also imply that people that are employed can enjoy more premium benefits of employment since they have additional income, such as traveling, entertainments, etc. The universal basic income does not mean you live the life you want, it means you get to live a life, but for people who wants a lifestyle with quality, they would have to be employed. Therefore, the policy of universal basic income doesn't discourage employment, rather encourages it. Other than this practical problem, I cannot think of anything else.