It's not even locked behind evil, it's locked behind a single decision where you have to give up a lot of content.
Eg why couldn't you convince the thieflings to leave, and then help the goblins slaughter the druids, lead by their corrupt leader or Convince the thieflings and goblins to join forces to slaughter the druids, later freeing them from the cult making them all owe you. or Spare her (which was a workaround apparently until they patched it out)
It's just lousy decision design. Consequences shouldn't be coupled together based on a single decision IF you want replay value. There should be room to mitigate each individual consequence whether it's tedious, difficult or luck based. For the most part, the game does this well but this one example is pretty bad (and to a lesser extent the Act 3 stuff is terribly all or nothing)
