From "Star Trek: The Next Generation: Lower Decks (#7.15)"
[Joret Dal explains why he is providing Starfleet with information about Cardassian strategic operations
All my life I've served in the military. Once, it was an institution dedicated to the security of Cardassia. Now, it's little more than a platform for ambitious guls hoping to make their reputations in battle. If the information I've provided helps Starfleet deter even one pointless skirmish, I've served my purpose.