As for the business of what would happen if someone wanted to cross the floor to the NDP - I guess the only consistent policy would be to ask that MP to sit as an independent, ...
Excuse me, but if someone is elected under the banner of (say) the Green Party, and they declare that they will now support the NDP, how can they sit as an "independent"? Why shouldn't they immediately resign and let their constituents decide? They weren't elected to sit as an "independent".
There seems to be a whole lot of confusion here as to what constitutes "principle".