The "small, radical, fringe parties" is just scare tactics by Liberals pushing Ranked Ballots. (Check the democracy.ca questions.) You can set minimum thresholds - e.g. with a 5% threshold, it would be interesting if the Greens would actually make the cut in Canada. Other methods like regional super-ridings of maybe 10 MPs would produce a higher threshold, though some small parties with concentrated areas of support might get a few members.