It's just a fundamentally flawed system since it's always easier to campaign AGAINST something instead of FOR something since the moment you make a constructive offer you're making yourself attachable while being destructive works without being open for attacks of any kind

Normally this can be resolved by there being too many parties and too many different viewpoints to oppose all of them without being crazy - but with just two parties it gets too easy to see every of those two as a single entity as and just oppose whatever they are doing