Government by first past the post is authoritarian

The difference between oligarchy and democracy is that with democracy the power is held equally among the people but with oligarchy power is restricted to a small number of people. Part of the problem with oligarchy is that this power which is held by the few can be purchased by the rich who seek to protect their interests so oligarchy tends to result in government by the rich, which is plutocracy. Oligarchies tend to result in plutocracy and this is why democracy is beneficial for the poor whose interests are opposed to those of the rich.

The first-past-the-post voting system is not full democracy and as such it is an oligarchy of the two main parties which will tend to result in plutocracy as the rich will purchase this power held by the two main parties. So we can say that fptp will degenerate from democracy to plutocracy.

Without government there are no objective property rights so it is not easy to envisage a civilised country without some form of a state but not all states need to be authoritarian and so then we can have a state which is consistent with anarchy in the sense of being without authority. If we use the word anarchy to mean only to be without authority then (proportional) democracy is consistent with anarchy. The state becomes authoritarian and opposed to anarchy if it does not use democracy and further if it does not use a proportional (or direct) form of democracy. Anarchists can accept democracy but not democracy which is not proportional, or direct. For this reason first-past-the-post is not anarchist, since it results in oligarchy and plutocracy, but proportional representation is anarchist, if anarchy can accept a non-authoritarian state.

Democracy is not always in opposition to anarchy, provided the voting system is helpful to voters but the first-past-the-post system is unhelpful to voters and as such it is always non-anarchist and therefore it is authoritarian.