Christianity condemns homosexual behavior - not the person - and considers such behavior sinful. Since all people are sinners (in some respect), all are welcome to be members & practitioners of the Faith. The welcome applies for all regardless of sinful behavior, be it murder, theft, lying, incest, pedophilia, adultery, etc., and homosexual behavior.
No one is forced to join, but membership has responsibilities regarding sin. They include: confession of committing the sin, acts of contrition & seeking forgiveness. Whether the behavior is driven by a genetic pre-disposition is irrelevant; people are considered to be more than beasts and are expected to be able to control their urges (just as they are with criminal behavior).