Some titles are capitalized, some are not. According to English.SE there are several styles.
Should we pick one or just follow the mood?
It seems to me like we have two main ways that people title their questions.
I don't think that the capitalization rules of questions are particularly important for us, though, and I don't know that we have to edit questions just to fix capitalization. I don't even think I really follow these guidlines myself. There might be times, though, where we would want to edit a question title to fix capitalization. Examples include if the OP leaves the word "I" or a proper noun uncapitalized. Maybe a good rule would be, if the capitalization scheme of a title feels "jarring", fix it. Otherwise, leave it.
I don't think there's anything wrong with having guidelines, but it's probably not worth our time to enforce them strictly.