The classical response to such an argument is to say that if something like vaccines are self-evidently good then we should not fear the promulgation of contrary opinions because their error will be self-evident.
However, "Killing unborn children is bad, because it is bad" and "Women having making medical decisions without government interference is good, because it it good." "The right to defend one's self using firearms is good, because it is good." "Giving people access to guns to kill other people is bad, because it is bad."