Political theory suggests that there are two ways to aggregate ideas and preferences. The first is through brokerage parties, of which the Liberal Party is a classic example. It is not an ideological party, but a “big tent” that forces members to compromise on preferences “within the family”. The Democratic Party and Republican Party have also been, traditionally, brokerage parties in the same way. However, the Republican Party has recently deviated from this path with moderates being forced out or to the fringes.
The other way to aggregate ideas is through a system that provides for coalition governance. Smaller parties that represent a narrower menu of ideas, sometimes holding a specific idea or ideology or, a special interest (see Green parties), are elected with only a handful of individual MPs. In order to form a government, the would-be-Prime Minister must cobble together any number of these smaller parties with a view to forming a stable administration. Israel is, of course, probably the best example of this, although it is also not uncommon in Germany and other European countries. Ideas are not so much aggregated within a party, but externally.
For decades, Canada has mostly been the former, so the question becomes, ‘should Canada gravitate toward the latter’? The advantage of the latter model is that compromises and machinations are often done in full view of the public, making the process more transparent. In addition, the parties within the coalition hold one another accountable, such that if the Prime Minister reneges on commitment A of Party X, Party X may fail to support a policy of the Leader’s party in response, or withdraw from the coalition altogether. See the Liberal Democrats refusal to support boundary redistribution in the UK. The advantage in the former arrangement is that it makes government more nimble, stable and predictable.
Since Pierre Elliott Trudeau, power in Canada has been gradually concentrated in the hands of the Prime Minister, to the extent at present where, not only are opposition MPs essentially toothless, so too, are members of the Prime Minister’s own governing caucus. The avenues of access to government have shrunken or disappeared. In Canada, no roads lead to Rome. This leads to an opaque and unaccountable government, which is less accessible to citizens and interest groups. A merger between the NDP and Liberals will not change this – it will make it worse.