My favourite political hobby horse.
I have no idea why people would oppose a preferential ballot. I understood why people were opposed to STV because it was somewhat complicated.
Right now people are complaining that 60% of voters opposed Stephen Harper. But his 40% this time is no different than any election since 1968 except for the Mulroney 50+% in 1984. 40% usually gives a majority. In fact, Joe Clark got a minority in '79 with 35% - 5% less than the second place Liberals.
A preferential ballot allows us to ensure that the person with the most support (not necessarily most votes) will represent each riding. Were the Conservatives the last choice of every voter? Probably not, I am guessing that several supporters of the fringe parties (Christian Heritage for one)and even many Liberals would have had the Conservatives as their second or third choice.
My best guess would be that the Conservatives would have ended up with a minority government which more closely reflects the wishes of the majority of voters. It would also have prevented the need for strategic voting. We could still vote for the party we support knowing that our second choice would support somebody we can tolerate if our first choice lost.