not only caste is based on birth, religion is also based on birth. after birth we start follow the principles and customs of religion as well as caste and in most of the cases we do not change our religion. we accept our religious belief without any arguments and without comparison with other religions.we take birth as a hindu, muslim, sikh, budhist ,christian etc. Without our wish we have to follow our religion from our childhood.
same is the case of caste but less customs & principle we have to follow to remain with particular caste. sometimes these principles are also not followed. caste related customs pertain to marriages, birth , death sanskar etc
there are several persons who do not write their caste with their name and are not happy to remain with their caste community because that community may have more restrictions to follow.for example some caste strictly follow the principle of different gotra marriage . if some person wants to disassociate himself from his caste community then he cannot do it legally .is it not against our natural right to choose our community as in case of our religion.