The system of PR was brought in for Welsh and Scottish parliaments as this is a system used in many countries, as thought of as somehow "fairer".
I've had many debates about this with people, and I would say that whilst it might work in places with two dominant parties, in the UK, as it has been in some European countries (Look at Italy) it would be disasterous, and anything but "fair" - I'll elaborate...
PR sounds on paper very very fair. Parties get the proportional amount of seats in parliament according to the number of votes cast - what can be fairer than that. But....and here is where we have to analyse it....PR being fair is one of those issues we have to give thought to. Like many popular things, it's very easy to kid the people into thinking it's fair, but this doesn't stand up to further scrutiny.
What will actually happen, is that the party with the most votes, in anything other than a country with two dominant parties, then a number of minor ones which would then get fair representation, will be unable to form a government. It is extremely unlikely in a country with more than two big parties that anyone would get enough for an absolute majority - ever. That party will have to find a coalition partner.
OK - sounds good so far, means one party can't dominate - but let's keep looking deeper.
So, depending on the votes proportion, one of three things will happen.
1 - The biggest party will find a smaller party to govern with. This then small minority party will be able to punch WAYYYYYYY above their weight. "we'll only support you if...." - and the party most people voted for will be blackmailed into carrying out things most people would not support. Anyone fancy the BNP having a say? Democratic? You decide.
2 - No-one can form a government, one party steps aside and says the other can form a minority government, then whenever the government tries to govern, they can get scuppered by the combined votes of the other parties. The country grinds to a halt. How can this be good?
3 - For this, I need to give the example of the UK. If the UK had PR, then no party would ever gain a majority ever again. Come on, they would have to have way over 55% of the support - it just doesn't happen in UK politics. Some years, Labour would have most votes, some years the Conservatives would have most votes. In every year, the LibDem party would have between 10 and 25% of the votes. What would then happen - and LibDem leaders have suggested this for long enough, is that they would be prepared to go into a coalition with Labour. Labour is a left wing party, and a fact some don't seem to realise - they are so often used as a "protest vote" - is that the LibDem is also a left wing party, in some cases more left wing than many Labour. They are like a social democratic party, but with pragmatism added, but anyway. Many Labour members would abhor this, quite a few Libs would prefer to be in partnership with the left wing of the Conservative party, but the majority view is that this is what would happen - always.
Now this is where it gets frankly very scary - think about what would happen. Unless people realised this, and support for the LibDems totally collapsed, then the government would always consist of a LibLab alliance. Labour would never be able to govern alone, the Tories would always be unable to govern, because the two left wing parties would coalition form.
Before any left wingers have a wet dream over this - think, and think real hard. For a democratic country to function, there has to be an opposition, and an opposition which has a chance of taking power. If not, then there is no check whatsoever to the government. Under PR, then it doesn't matter how unpopular the government becomes - it would be near impossible to vote them out! There would always be a LibLab alliance - near dictatorship in a way.
Yes, first past the post is really unfair. 40% of the vote is enough to decide a government. In many constituencies, the vote majority for a party is in the 1000's - but they elect one MP, just as a majority of 2 is enough to elect one MP. In many areas it doesn't matter who you vote for - one party will get in because of that parties support in that area - but it has one big advantage - it means there will be stable government. It means there is a real chance they can be voted out - and this will keep politicians in check. It means that tiny minorty parties can't dictate their often sour views - the tail cannot wag the dog.
Only one big party is in favour of PR - the minority LibDem party. Wonder why