The caste system according to ancient text Manusmriti states that caste is assigned based on attaining spritiual knowledge, it can go up with increased knowledge and go down with pride. But in the caste system today, they assign caste based on birth and bloodline. And that is why many lower caste Hindus convert to escape the caste system(although they are still looked down even after they convert). The people who get offended by conversions are the ones responsible for them.