The growth of Knowledge consists of correcting misconceptions in our theories. Ever since the Enlightenment this had happened through a tradition of criticism. New explanations are proposed, criticized, and then refined. Since the tradition of Conjecture and criticism has created all Knowledge and Progress it's absolutely imperative that we keep it. Free speech is critical. No idea should be beyond criticism.
The theory that all knowledge is derived from sense-experience (i.e. from experimentation). When empiricism was first introduced it played a positive role for Progress by providing a defence against traditional authorities and dogma. All claims of the supernatural now had to be backed up by hard evidence, which meant that 'provable' science superseded religious mysticism and superstition.
There are only two known sources of knowledge creation: Biological Evolution and the thoughts of People. They have some key differences. In the case of human knowledge, the variation is by Conjecture, and the selection is by Criticism and experiment. In the biosphere, the variation consists of mutations (random changes) in genes, and natural selection favors the variants that most improve the ability of their organisms to reproduce, thus causing those variant genes to spread through the population.
Moral philosophy is basically about the problem of what to do next–and, more generally, what sort of life to lead, and what sort of world to want. Morality is a type of Knowledge. This means that moral 'truths' can be discovered by the usual methods of reason, which are essentially the same as those of science (although there are important differences).