In my opinion, there are many things wrong with mixed proportional systems.
The constituencies become much larger. This may not seem like a problem in relatively homogeneous urban areas, but when you merge 2 to 5 rural areas into one super-riding, you lose representation, especially if the super-riding is dominated by a medium sized city 3 hours away. Rather than having an MP to represent, for example, 100,000, that MP will represent 300,000 or more.
True, constituencies do become larger but it doesn't mean less representation. Under the mixed proportional system that I'm proposing, ideologically divided ridings could be represented by more than one MP (2 or 3 MPs per "divided" riding; I'll describe this system in a bit more detail below). Plus, look at our present system; sure your MP might represent only 100,000 people, but if you didn't vote for that MP does that MP really represent you and your political views. And if that MP got elected with only 40% of the vote, how well does that MP represent the majority of electors in the riding who didn't vote for him or her? Now they want to add more seats; this will only add to the number of backbenchers who really don't do much; how well do you think backbenchers represent the people in their ridings, even within their own party caucus?
You still have "list candidates" not voted directly by constituents, but elected via proportional representation. In other countries, these pols may be unpopular amongst the voters, yet due to their ties to the party, they could be the first candidate on the list to be elected on proportional lists.
I agree with you there, lists are not the way to go, but proportional representation does not necessarily mean lists of candidates. Under the mixed system that I would propose, winning candidates would gain their seats just as is done today under our existing system, and the remainder of the seats would be filled using those candidates that did not come in first place in their ridings but who nevertheless got the most votes for their party. In other words, in a highly contested riding, two or three candidates might still end up with seats; one for winning the election in the riding, and the other(s) to make up a party's proportion of seats because they got the most votes for their party. Highly divided ridings get more representation while highly homogeneous ridings get 1 MP because they don't need more. Compared to party lists, under this system that I am proposing, people actually have a say as to whom might represent them one way or the other.
You also get the fringe party tail wagging the mainstream party dog. In many countries, mainstream centre-left and centre-right parties have to form coalitions with extremist parties to form government. This often ends up with small unpopular extremist parties getting disproportionate power in setting policy relative to their popular vote with predictable results.
A mixed system would still favour the more popular parties as fringe parties would sort of get the left overs. Also, the more people realize that their vote counts for something - as under a system that features proportional representation - the less likely they are to vote for fringe parties.
Talking to people in New Zealand where they have MMP, most said they would like to go back to the old First Past the Post system. They say government has become a gong show since they adopted that system because every special interest group now has a party and it is relatively easy to get at least one seat in Parliament.
The major drawback of proportional systems has always been minority governments and in many parts of the world this means instability. But this is not true everywhere; there are some countries where minority governments are a fact of life but they are still able to make accommodations and function effectively. The most important thing is leadership; a minority government lead by an able leader can find accommodation with other parties and make government work. And this is exactly what Canadians want from their political leaders. We are an idealogically diverse nation and we want that diversity to be represented in the House of Commons, but we also want our leaders to work together to find common ground. What we don't want is one "minority" group ruling over the others for four to five years.
IMHO, our system isn't perfect, but it's better than the others that have been tried.
IMHO, our present electoral system is far from perfect, and not everything has been tried. What I'm proposing is not really a radical change, simply a change for the better.