double-edged sword

noun2

1. •
   (figurative) A benefit that is also a liability, especially a benefit that carries some significant but not-so-obvious cost or risk.

   • He added: “Facebook is a double-edged sword. You don’t want to support it, but you have to use it in order to reach a large audience.” — 2020
2. •
   (figurative) A neutral principle that has applications that may be either positive (beneficial) or negative (adverse) to one's own interests.

   • The unintended ambiguity of the phrase was a double-edged sword: it spurred litigation but it also ended up shielding good-faith actors.