So I'm going to be a DM for the first time this week, and I've been making a low fantasy campaign setting based on English history and medieval romances. I've been telling my friends about it and whenever I mention that either my setting doesn't have tieflings or Dragonborn or that Elves and Dwarves are rare and are not trusted by humans they always go "you should let the players be whatever they want" or "why are you going to have humans be antagonistic to elves" or that I'm railroading them. Am I being a bad DM despite going for a specific genre?

​

Edit: Grammar and I just want to clarify that I have talked about my setting and restrictions with all the people I want to play with. Half of them are into it and it's the other half that have made the comments I mentioned, as well as the friends I was asking for advice.