No—plain, unsalted cashews are not generally considered bad for health. Cashews are tree nuts, and nuts provide unsaturated fat, protein, and other nutrients; research summarized by Harvard’s Nutrition Source associates regular nut consumption with lower cardiovascular risk, although this is an association rather than a guarantee.
Choose reasonable portions and be cautious with versions coated in sugar, chocolate, or lots of salt, which can add calories, sugar, or sodium. Anyone with a tree-nut allergy should avoid cashews and follow medical advice.
Source: Nuts for the Heart — Harvard T.H. Chan School of Public Health