Single winner seats give strength to the dominant parties

In majoritarian voting systems, it makes sense to cast your vote for one of the leading candidates; there is no point choosing a minority candidate because there is no chance this vote will count, it is better to influence the outcome between the favourites.

The leading candidates will generally be those endorsed by the main parties, and it is due to this dynamic that political parties emerge. This means that, in choosing their candidate, the main parties have an effective (if not in fact) monopoly on what might be termed the centre-right and centre-left. There would be less need for strong political parties if voters could be assured that a vote for a minority candidate would not be wasted. To enable this, it makes sense to allow more than one winner from each seat to be promoted to parliament. If there is more than one winner a vote cast for a minority candidate has a chance of success.

Proportional representation enables votes cast for minority candidates to be meaningful and as a result, this weakens the power of the main parties of both left and right. It is less vital for politicians to be part of the elite.

If candidates are being chosen for a representative position, such as parliament and not something presidential like being a mayor, then we can have constituencies with more than one representative, in a sense a parliament of parliaments.

One of the features of Democracy is that it tends to accentuate ignorances; if, among a large field, most of the candidates represent the truth and respect individual rights then there will be nothing to choose between them and it might be that none of them emerge as a potential winner and the vote will be split. If one of the candidates is ignorant in a manner held by a number of others who are voting, this politician will win, even with a small following.

If there are to be more than one winner chosen from the seat then this is helpful to the 'reasonable' candidates, they are not required to pander to the incumbent elite party who are seen as the natural opposition to ignorance.