Here's a poser for you - is it better (read: more effective) to oppose a policy as being unethical or as being incompetent?
Oh hai, moral high ground
Ethical arguments depend on your audience accepting the terms of your position.
Underpinning opposition to the bedroom tax, the privatization of the Royal Mail or badger culling, say, are shared assumptions about human dignity, public services and animal rights which are commonplace among progressives. It's not that the evidence isn't there to back up these positions - quite the contrary in fact - but that the arguments expressed are generally value-driven, in the manner of self-evident truths.
It can be tremendously powerful to tell your truths and find them affirmed.
But if your audience rejects those assumptions - advancing others - what does that do the force of your arguments? Will you be heard outside your social media echo chamber?
Is outrage enough?
A better mousetrap?
Or will you instead, more calculating, keep your values in the background hone in on the fact that a policy just plain isn't working? It doesn't matter if your target disagrees with you on the big questions -- the role of the market in the public sector and the futures of farming and housing provision - as long as you can agree on an 'objective', factual analysis of a specific situation.
Unlikely bedfellows can line up behind a shared evidence-based position - just look at the breadth of the coalition which supported a 2030 decarbonisation target in the 2013 Energy Bill.
But arguing from competence alone does not make the heart-beat faster. It risks being privilege (technical knowledge) speaking to privilege in its own idiolect. It also assumes your audience are members of the reality-based community.
And it does not disrupt the political narrative, illuminate and seek to resolve deeper problems, in the same way that values-based arguments do. Alone, the rhetoric of competence and incompetence risks bringing us to Deng Xiaoping's 'It doesn't matter whether a cat is white or black, as long as it catches mice.' See the continued existence of the House of Lords as a case in point.
Dude, it's situational
Of course it is. And I'm presenting ideal types here: in practice our arguments combine evidence and ethics to varying degrees. I also haven't talked about how the language we choose might depend on the opportunities open to us and the power we wield.
But I think it's valuable in itself to recognise how we express ourselves as campaigners, the extent to which we tend towards one pole or the other, and the perks and pitfalls of both.
And speaking personally, I'd love to read more from the activist community that is a high quality synthesis of both. Recommendations in the comments section please. :-)