It happened again in Madrid a few weeks ago. I was at a meeting of development officials and researchers and Venezuela came up in conversation. Cue mayhem. Is it possible to mention Hugo Chávez without becoming embroiled in name-calling, exaggerations and, not infrequently, brazen lies?

While it is fairly normal that politics can become partisan very quickly (just look at the US at the moment), the point of being a development professional is meant to be that you step outside the partisan for a minute to examine, wait for it, the evidence. I don't claim that this is easy, because evidence can be skewed by its provider (often, in international development, the government of the country in question). But that is the objective.

So I am constantly surprised how many development professionals find it hard to do this when Venezuela gets mentioned, or Cuba, or Bolivia. It is as if evidence and balanced analysis are appropriate for some governments but not for others.

If you say, "inequality appears to have gone down considerably in Venezuela", you risk being accused of being a Chavista. But if you say, "inequality appears to have gone down in Ethiopia", no one would start accusing you of being a zealous supporter of Meles Zenawi.

The same problem exists on the other side too. When I was in Colombia, some in the human rights community were incapable of saying anything positive about the administration of President Alvaro Uribe, because they accused his government of making shady deals with paramilitaries.

I would call this the "pitchfork effect" (technically known as the "e-halo effect"), whereby a leader can become so demonised in certain countries or populations that it is no longer possible to assess their achievements and failures in a balanced way. The more a leader is demonised, the more his or her supporters will exaggerate how wonderful they are.

It is the converse of the more well-known "halo effect", whose most famous beneficiary in recent times was Nelson Mandela, a politician to his fingertips, embroiled in many of the things politicians get embroiled in, and responsible for as many bad decisions as good ones on economic policy in South Africa. But criticise him and you are criticising the freedom that he personifies. It is a handy effect to have.

There are some leaders who are so vile that applying a balanced assessment to them seems tasteless. The murderous juntas of Argentina and Chile in the 70s and 80s spring to mind. But even Augusto Pinochet, a man who oversaw barbaric murders and torture, appears to be granted by many a balanced assessment of the time he was in power. And that is probably right. It is not condoning his actions to assess how his period in power affected Chile's economic conditions.

So why not Chávez? One word often used to describe him is "dangerous", and this may be the key to understanding the rage he engenders. It is hard to consider him a military threat, the odd phoney war with neighbouring Colombia notwithstanding. No, it is the danger he poses to normality that people who oppose his policies find so worrying. His rhetorical attack on modern capitalism is so strong, that were he to demonstrate any improvements in Venezuela with his rather vague "21st-century socialism", the conventional wisdom favouring free markets and a limited state would be challenged. It is the same reason that the US is so obsessed with Cuba – the danger to capitalism is allowing another model to succeed.

I am saying all this because the first step we need to take when analysing the achievements and failures of the new left in Latin America is to do our best to be balanced, taking the evidence as we find it, and trying to incorporate new evidence into our analysis, even if it does not fit our assumptions.