As it turns out I'm not very good at this whole political party thing. But if you were going to join a political party, you might want to read the fine print. For most, you are not allowed to join more than one. Which is annoying, my personal opinions don't fit nicely into a party. The prospect of being in more than one party could be interesting.
So I asked the parties why I can't join more than one and after several months I got a couple of answers by email.
The reason we ask that you not retain other memberships in other provincial or federal party’s is because as a member of the NDP you may be privy to sensitive information about both donors, member details and election planning.
BC NDP party
It is a party constitutional requirement.
BC Liberal party
Apparently the numbers of people actually in political parties are quite small. A similar problem exists in the UK where numbers have been falling over the years. In Canada:
Of the eight to ten per cent of Canadians who were engaged more robustly in election campaigns, only about 1-2% per cent were consistently active members of a party, placing Canada at the bottom of the list of Western democracies.