Paul Martin, arguably the most rightwing Finance Minister in Canadian history, made the tax system much more regressive and massively gutted social programs. The NDP, including Layton, has rightly blasted the Liberals (and the Tories) for that. So if the tax system was so unfair, why wouldn't the NDP support an increase in taxes on corporations and the wealthy?
Because the NDP loves to cry about what the right does at the time, but doesn't actually oppose what they do to the point of wanting to reverse them when they get the chance.
It has to be either a lack of principle or a lack of courage.