Didn't McCoy say damn it a couple of times in TOS? I know they certainly dropped some cursing in the movies so it's not like Trek hasn't cursed before.
I don't think he ever did in the original show, which is crazy, because saying "damn" feels so in character for Bones that it feels weird to think he never uttered it in TOS.
Which makes me wonder if there were fans that hated seeing the TOS films feature language merely because they're too used to the original show not featuring it. I have to assume because if I've learned anything about fandom is that doing something different is always a bad thing.