This is a problem that should not be 'taken lightly'. [=this is a problem that should be treated seriously]
Considering the harm he did, he's 'gotten off lightly' with only a warning.
Our troops were armed too 'lightly' to take on the heavily armed invaders.
(..) You know I'm not very happy with them either. Katniss... This is serious. Not just for you. They don't take this things lightly. You say you couldn't help yourself. You're so in love with this boy that the dark have not with the most... Unthinkable... (..)2012 The Hunger Games