Let's say the Liberals win with 45% of the vote, the Greens get 7%. The Liberals require Green support to pass legislation, they are effectively held hostage by the Greens. 7% of the electorate that voted Green is massively over represented in legislation.
My worry with pure proportional representation is that we will end up with the current parties for a while, then they will start to split. We will have
- 2 conservative parties from the current one
- NDP will split between old school union NDP'ers and new school Naomi Klein style social issue NDP'ers
- emergence of ethnic parties in certain regions of Canada. No reason why the 'Pan-Asian' party could not win in parts of Vancouver
Without a good national discussion and thing about the outcomes, we risk putting Canadian politics down the road of ruin.
Sorry, but to me, this is panacea.
Splitting current parties into smaller interest groups is what democracy is all about - giving those interest groups the means to actually win a seat in parliament, so much the better.
Your example with the Greens holding the Liberals to ransom is flawed. It ignores the fact that there are other parties with seats with which to form a coalition and push legislation through. If the Greens can't be pulled on side, the party in government (the most seats) has the choice of modifying a bill to meet the Greens halfway, or finding another party (Con, NDP, Bloc, other) to support them.
Prop rep almost always result in minority governments, and minority governments almost always force more cooperation between parties, thus representing more voters.
When one person suffers from a delusion, it is called insanity.
When many people suffer from a delusion, it is called religion.