I think the most obvious semi-basilisk example is certain strains of religion. Insofar as it makes you believe you might go to hell, and all your friends are going to hell, these religions will make you feel bad an also make you want to spread them to everyone you know. Feeling bad is not the same as death or mental breakdown or other theoretical actual basilisk consequences but in essence there are meme complexes that contain elements that demand you spread the whole complex. If someone's in possession of such a concept but has defeated it or is in some way immune it may still be correct for them not to tell you for fear you are not and will spread it to others once it has worked it's will on you.