double edge sword

Noun

double-edged sword (plural double-edged swords)

1. (figuratively) 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 June 23, Tiffany Hsu, “Ad Boycott of Facebook Keeps Growing”, in The New York Times, archived from the original on 15 Mar 2021

   Synonyms:

   dual-edged sword, two-edged sword

2. (figuratively) 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.
3. Used other than figuratively or idiomatically: see double-edged, sword.