Various religions' scriptures describe same gender sexual relationships as going against God's commandments. For many religions sex should always be associated with the possibility of procreation (conceiving children), which is seen as natural. Same gender sexual relationships are therefore described as unnatural and forbidden.
However, there are many religious believers today who take different views. Some would say that it is only the sexual act which is forbidden, and being attracted to someone of the same gender is not sinful in itself. Others think that today we have a better understanding of same gender relationships than people did in the past. They might say that many are born with such attractions, which for them are natural and that it is not necessarily something about which people have any choice and so they ought not to be condemned.