Why do people evade the evidence?

I was struck by this article: Killer syndrome: The Aids denialists

I did not realise that there was still an argument against the HIV/AIDS link and that retroviral medication has given longer life to many. The methods seem to be the same as those that are used by many people who suggest global warming is a hoax. I am trying to think symmetrically about this by asking myself – why do I accept the evidence? I have started that on my page Climate Change. It is easy to get locked into a position and to cease thinking laterally.

I found responses to the news that UEA CRU had disposed of raw data used for the temperature estimates about twenty years ago, Climate change data dumped, fascinating in this respect. This particular news item is mentioned a lot of times, if you check in Google, as showing that the scientists were destroying evidence that would show them biased. There is rare mention that a lot of data is being lost all the time. NASA cannot even read the data tapes recorded decades ago because the tape readers are gone. I remember in the mid 1980s buying a 20 MB hard disk that cost as much as four or five good specification complete computers now. I would always like to keep all the data, but I can understand that some people will want to tidy up with no bad intent.

Science is not about certainty or perfection; it is a way of collecting and assessing evidence about the world.