Morality is not conscience. Morality is a collection of generally accepted principles, that is, principles that are accepted in society, some kind of association of people. Moral principles are not laws, laws determine the punishment for violation of laws, and for violation of moral principles there is only one punishment - public condemnation, that is, condemnation by other members of society. Consequently, condemnation is limited to society. Each community of people has its morality.
Over time, morality, a collection of moral principles, can change, be supplemented by new principles, or some principles can be excluded. The principles that are adopted by the conscience of one person may coincide with generally accepted moral principles, or they may differ. If the generally accepted principles differ more from the principles of conscience than coincide, then I see two ways for such a situation to develop, either the principles of conscience are replaced by generally accepted ones, or a person will have to leave such a society so as not to torment his conscience. Leaving society is an extraordinary step, not everyone has the willpower sufficient to leave society, and some choose the path of a martyr, prefer to torment their conscience, do not change their principles, and do not accept generally accepted ones.
The generally accepted principles and principles of conscience have a common feature; they can change under the influence of external conditions. When it is comfortable, society and a person can collect a large load of moral principles - to raise the level of morality, and under the influence of a threat, they get rid of unnecessary principles - lower the level of morality.
Like any other organism, a person is looking for his place under the sun, and if something threatens this place, then he needs to look for another place under the sun or fight for what he has found. In such a struggle, a person lowers the number of his principles, uses the adage "in war, all means are good." If such a struggle becomes generally accepted, that is, everyone must fight for their place under the sun, then society will get rid of generally accepted moral principles.