Oh I agree that it's a poor argument, which is why I was curious as to why it remained on the League's website for so long.
I'm having trouble understanding how inertia is a better argument. True, Canada has always been a monarchy, but until 1919, women in Canada had never had universal suffrage; until 1948, countries had always been allowed by convention to invade and annex other countries; until 1865, Americans had always owned slaves.
The argument that since something is the way it is then it is therefore the only way it should ever be is dangerous fallacious.
Instead of pining away for the good old days when Canada has always been a monarchy, why not look forward to how the monarchy will continue to serve, represent and unite Canadians?