没什么不好，想quit找工作或者转专业，系里/导师应该都会理解。我之前的专业网站上也写明了：A student who is admitted to the Ph.D. program may decide, some time during the first or second year, that they do not wish to get a Ph.D., in which case they can complete the course requirements of the M.A. specialization they choose and take the M.A. exam.