Is it Islamically permissible to insist on marrying a fiancé afflicted with a rare disease – one that has the potential to deteriorate and affect his senses or sexual capabilities – based on having a good opinion of Allah, the righteousness of the fiancé, and the experiences of Istikhara?

If the man you wish to marry has a defect, and your guardian objects to your marriage to him, and you are unable to convince him, then the guardian's word is to be considered, as the jurists have stipulated that the guardian's right remains in this situation. The guardian often views the woman's best interest with a wisdom that is more far-sighted than her own. Therefore, it is best to disregard this man and ask Allah to grant you someone better than him, while having a good opinion of Allah and entrusting the matter to Him, citing the verse: "And perhaps you dislike a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah knows, while you know not."