First past the post is left wing

A statement of Duverger's law is as follows: "Single-member-district electoral systems that require only a plurality to win election tend to produce two-party systems, whereas proportional-representation systems tend to produce multiparty systems..."

Given that this is true it might be possible to further speculate about the nature of those two parties and which kind of party is favoured by first-past-the-post.

If we accept that first-past-the-post results in a two-party system then (to use the established vernacular) one of these parties will likely be of the 'left' and the other will be of the 'right', with right-wing meaning that the particular party favours the market over the state. The left-wing party is more in favour of the state than the right-wing party. But if we examine the attitudes and behaviours of the voters it is likely (at least to my eyes) that a right-wing voter will find more to object to with this system because they are by nature more critical of the government. A left-wing voter is more tolerant of policies which they do not agree with being held by their party of choice because they understand that for the state to be large people must make compromises. I am not making a value judgement here about which attitude is favourable, I am merely making the case that left and right-wing voters are not symmetrical in their attitudes to government and their chosen political party.

Right-wing voters are much more likely to object to being 'forced' (expected?) to vote for a monopolistic right-wing party (as a consequence of Duverger's law) than the left because they by nature approve of choice in the market and presumably in the ballot box. It is more consistent for the left to tolerate something they might not choose for the greater benefit of the group and the state. So first-past-the-post is less offensive to the left because the compromises arising from a lack of realistic choice are less onerous given that they will generally be willing to make compromises for the state, and so they will be more loyal to the established party of the left.

People on the right will be less likely to remain loyal to the established party of the right because they are already predisposed to be oppositional with regard to the government. This is why first-past-the-post not only favours a two-party system but it further favours the party of the left.