What is the mindset of people who sign these letters? Presumably someone like Tim Minchin has thought to himself that because he can make amusing comic routines about religion and blow up dolls, that adding his signature to a letter will somehow add weight and merit to the cause he believes in. It doesn't, it just makes him look pompous and egotistical and would do regardless of the merit of the argument being put forward. The same applies to the rest of the figures who signed the letter.
* On the subject of CJ De Mooi from Eggheads, judging by the wikipedia entry on him, he is every bit as smug as he appears on television:
He adopted the name de Mooi when modelling; he translates it as Dutch for "handsome man", though a more literal translation would be "the beautiful".Bell end.