So what are the issues with first-past-the-post?
Canada is a great country to live in. Our political system has served us well. But as our country changes with more diversity and more political parties the system put in place in 1867 is showing serious problems with fairness.
Winning an election without popular support.
FPTP works great when there are only two political parties. The candidate with the most votes will always have the support of more than 50% of the voters. This was the case in Canada from 1872 to 1921.
Since then there have always been at least three parties in Canada and usually many more. With three evenly split parties an election can be won with just 34% of the popular vote. That means 66% of the voters did not prefer the winner! Something close to this happens regularly in Canada.
Strategic Voting as a demoralizer.
Strategic voting is when you vote for someone not because you prefer them but because you're afraid that someone whom you like even less will win the election.
This gives the voter a mental conflict: You want to vote, but you don't like who you will vote for, so why bother voting at all?
Forcing citizens to vote for someone they don't like is even a common tactic in totalitarian systems. It is used as a means to demoralize and control the citizens, detect dissent, and discredit democracy.
Election results don't match the popular vote.
In our most recent 2015 election the Liberal party won 54.4% of the seats, an absolute majority in the House of Commons, but only received 39.5% of the vote. And that 39.5% includes strategic voters who would have voted differently if they had a better voting system.
In the reverse problem, the Green party elected just 0.3% of the MPs but had 3.5% of the vote, gaining much less power than implied by their voting strength.
Having a better balance of voting results and political power will make our electoral system fairer.
We don't even know what the popular vote is.
Because of strategic voting some parties get more votes than they otherwise would, and some get less. The end result is that we don't really know how Canadians wanted to vote, we only know how they actually voted. This makes it impossible to use the vote totals in a Canadian election to determine the real popular vote.
Power gets excessively concentrated.
With FPTP, the governing party often has more MPs in the Commons than is warranted by their popular vote. This often results in a majority government that is able to pass any desired legislation even though much less than 50% of the citizens voted for the governing party.