If we had PR all the major parties would fracture into smaller ones. It would be impossible for voters to know how to vote if for example they wished to kick out the government.
All that happens is a reshuffle and the same people come back to power in a different mix in PR countries. It is nearly impossible to dismiss a bad government. Corruption inevitably digs in.
Small parties (counter-intuitively) have far more impact in FPTP countries. If a small party finds a vote-pulling formula, the big ones have to copy it quickly. They have to keep their big tents full, or lose elections.
As a result in Britain the Referendum party was able to lever all the other parties into promising a Referendum on the Euro. Germany and France had similar anti-Euro parties, but they were completely ignored by their ruling coalitions.
UKIP’s offer of a referendum on the Constitution was matched by Michael Howard in similar vein, forcing Blair to follow suit. If we were a PR country, Blair could have ignored the challenge and pushed ratification through parliament.
The theory of the ‘fairness’ of PR systems is not matched in practice. Voters cannot vote a government into power or out of power. The shape of a government is decided by horse-trading between established politicians who trade policies for power after the lection is over, the voter having no part in the process. The voter is disempowered.