The state is invalid if it does not use pr

For a legislature to be accountable and to have a mandate from the people requires that it is democratic. Without democracy no government can claim to be legitimate and to have the consent of the governed. To be a government and to be legitimate requires democracy and elections. But if the elections are not proportional it is possible for people to make the (valid) claim that they have not been consulted and so they have not given their consent. To have valid and accountable government requires both democracy and also proportional democracy. First past the post is not enough to give a government (a legislature) legitimacy. To have legitimacy a government must use pr. If it does not use pr then a government has no mandate to rule and is invalid. To be valid a government must use pr. Only if it uses pr can a government be said to be valid.