5ed does a poor job here - the Paladin blurb is "anti Evil" but there is nothing saying that I can't be a Paladin of Vengence, my particular beef being against the Seldarine in general - for chasing grandma into the Underdark, or Correlon Larethian in particular - for taking my god's eye out.
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I would argue that that's a feature, not a bug. 5e is clearly presented as wanting to provide a lot of openness and freedom for players. If what you described is what a player wants to play, and everyone at the table is okay with it, then what's the issue? That's a very interesting and fun story potentially.
