What is Truth's view of the philosopher's stone? In an episode Father mentioned that "playing god" was a sin in Truth's eyes. Why doesn't Truth punish alchemists merely for creating or using a philosopher's stone then?
This question does not have a straightforward answer: the only normal alchemist we ever see making philosopher's stones is Dr. Marcoh, and it does not look like he has ever actually seen Truth, based on the Q&A "Wasn't Dr Marco a sacrifice?". It is also doubtful whether or not the alchemist who created the artificial humans towards the end of the series ever saw the Gate; if he did, the homunculi would have had an additional candidate for the fifth sacrifice, but they only mention alchemists that the readers or viewers have already met at that point, none of whom would have seen the Gate. Similarly, Shou Tucker's experimentation on his wife and daughter surely should count as a form of human transmutation, but his body appears to be intact.
My guess would be that "playing God" is mostly at stake in attempted resurrections of the dead because the alchemist there is trying to reverse death, which is meant to be impossible. (Some posters in this Reddit thread on Shou Tucker argue similarly.) Those other transmutations that one might consider to be "playing God" might be morally suspect (much much more so than trying to resurrect a loved one), but they do not transgress the boundaries of life and death and attempt to reverse the natural flow from life to death in quite the same way.