Like you said, all humans are flawed, no one is perfect. Monuments and other forms of tribute are used to reward a specific heroic act or achievements. It doesn't really matter if the person is ill-mannered or not, it is just to remember the achievement of the person. Moreover, they were just humans who tried to do the best they could with available resources and knowledge they hand at hand in their time.
RE: When History’s Heroes Fail the Present