Interesting... I have a slightly different understanding of the phrase "I'd hate to think..." from David and Bruce although my understanding is pretty close to David's. "I'd hate to think X" is a contraction for "I would hate to think X" which means "I would really be unhappy if I thought X was true". It's important to note that the speaker is conceding that X might actually be true and is expressing his distaste for the possibility that X might be true. Examples: 1) I'd hate to think that my students care more about their grades than about actually learning the subject matter. 2) I'd hate to think that my children would rather eat junk food than the nutritious meals that I spend hours cooking for them. 3) I'd hate to think that you have been copying your homework from a classmate instead of doing it yourself.

without looking it up I think that this expression really started out being: I hate to think But they come down to the same thing really - that the idea of picturing the consequences of something would cause mental pain! Since you can imagine yourself taking some kind of pre-emptive strike on the situation the expression: Perish the thought comes down to pretty much the same thing. Since I hate to think of it why not destroy it completely. Perish the thought has a bit of humour added to it since it is dramatically worked. It doesn't bear thinking -- would be much the same as I hate to think. Let's not even go there -- would be a very informal way of saying it, though this would be more like "I don't want to talk and think about it with you." It really means, the idea of what could happen is such that I would rather not think about it. Now, I realise that all my explanations need more English knowledge than the first statement. It just means "I don't want to think about it" Now why didn't I say that in the first place?!!

I'd hate to think (rewritten) It would be disappointing if ... I would be unreasonable if... It is highly unlikely that... You could improve upon that by... That is not acceptable... I would prefer to...