Illusions about the things of this world do not concern their existence, but their value.
Keeping a proper perspective about the value of the things around us — the everyday things in our lives, the this and that which are so much more than merely this and that — is probably made both easier and more difficult by the simple fact of having a family. Children and a spouse create routine, and routine risks monotony.
Therein lies the danger.
Saturday morning — breakfast, Skyping with Dziadek and Babcia, taking L to ballet, cleaning the house, doing the laundry, planning for the next week of school, correcting this or that assignment. This mix of truly the meaningful with the truly mundane risks making it all seem mundane.
Therein lines the illusion.
Weil is speaking the illusion that makes actions of inherent evil seem good in some circumstances, but the reverse is equally likely, and probably equally dangerous.