Causing the biggest genocide in the history of mankind which also happens to involve mostly Bretonians on the death count.
Invading Edinburgh and trying to settle in Gaia, the one place Gaians don't want people to settle in.
Killing tons of Gaians while trying to settle Gaia and during the war in Taus.
Pick one, any of these or all should be enough reason for Gaians volunteering with Maquis to brutally murder Royalist remnants. Also all of this happened off-screen for you, as you already left Disco by then I believe.
