From Longman Dictionary of Contemporary EnglishI hate to think what/how/where etcI hate to think what/how/where etcspokenHAPPEN used when you feel sure that something would have a bad result, or when an idea is unpleasant to think about I hate to think what would have happened if you hadn’t called the police. → hate
Examples from the Corpus
I hate to think what/how/where etc• But take care of them, darling. I hate to think what we'd do if they had to be replaced. 