>I frequently see remarks like 'Simon Peyton-Jones, great talk about Haskell but why did he use Comic Sans?' but nobody's ever been able to tell me what is wrong with it. It's a nice legible font, I like it. So until somebody explains to me ...

Of all the little things that annoy me about Comic Sans, this is by far the worst.

Suppose I showed some of my Haskell code to a group of people and they all told me that every Haskell expert says I should keep my IO functions as minimal and separate as I can. I ask them why, and they assure me again that Simon Peyton-Jones himself is adamant about this, but none of them seem to be able to put an explanation into words.

I wouldn't just dismiss them with "it works fine for me" and not even bother to Google something like "haskell separate impure code". So why do so many people do that when the advice is coming from designers instead of engineers?