Pr reduces the size of the state

Democracy is the only thing which reduces the power of the government. The government can do whatever it likes provided it has a democratic mandate... which means that only democracy constrains government. That being said (and assuming we want a small government) then we would want to have the greatest amount of democracy possible to be consistent. First past the post is a problem because it is not democratic which means the government is not sufficiently constrained. Fptp does constrain the government to some degree but pr would be more effective. If there is more democracy it is harder for the government to do what they want. If we have more choice there is inevitably less government because even if people want some government (and are in some respects a socialist) this doesn't mean they are a socialist in all regards. For example they may want free schools but not free police... with fptp it is likely that such a voter would be 'compelled' to endorse both of these things. With pr they can select only the socialism they want... which produces a reduced state. Pr makes the state smaller because people have more choice about what kind of socialism they want.