Actually, I do have a rule to address that: If one of you wants to rush the wedding... tough cookies. I have yet to meet someone who can hold it together for 6 full months without "warning signs".
But *way* too often the other party ignores these warning signs because their heart was already too invested. If you find yourself making excuses for your future mate or covering up their behavior, you're with the wrong person and (on some level) you do know that.
Again, you have to be honest with yourself.
You are, of course, correct. I have observed, however, that sometimes the bad behavior occurs in private and when the doubting partner tries to get some confirmation of their doubts everyone pooh-poohs them with the "He/she's such a terrific person!"