What about people who date few individuals (2-3), break up 1-2 times and their partners were neither closet racists nor violent nor anything that grave. That would describe majority of people I know.
well, the definition of a "fatal flaw" depends on the individual. even falling "out of love" with someone is obviously a fatal flaw which is probably the most common.
Falling out of love is big deal and reason to split, but hardly reflects badly on partners character the way racism and violence does.
If you are neat freak and she is systematically messy, than the relationship is bound to break or be lifelong hell. However, it is no violence and both partners can move to different successful long term relationship (this time being smarter and checking cleanness standards compatibility before first kiss).