You don't have to convince me that human rights are bad in Iran. I absolutely agree with you on that.
Where I do think the discussion at a foreign policy level is useful is that from my perspective, there's nothing to gain from shunning a country like Iran. It is a nice pat on the back to say we are taking a principled stand and we're not talking to that regime, but there are things to talk about with that regime. It's an absolute cliché to say it, but we talked to the Soviet Union during the Cold War, and there were things to talk about.
Engagement...and I'm not a member of the Liberal Party and I'm not endorsing them politically, but on a technical basis, I do agree with what was said on multiple occasions that engagement doesn't mean agreement. The point of diplomacy is to discuss things we disagree with.