At an individual level, one could be a good husband and father and be non-monogamous. At an individual level, one could also be a good monogamous husband and father. I agree with you there, although I think the expectations for most (but not all) people in western nations is that their wife/husband will be "faithful" in the traditional sense. If most wives expect most husbands to be monogomous, it starts to look like the _average_ person who is "unfaithful" is a "bad" husband by definition of the wife (even if they care deeply for their wife and any children). This also suffers from the network effect that even if the wife is ok with non-monogamy, family and friends could still shame her into being negatively effected by any non-monogamous actions in the marriage.

At a population level, it's hardly even up for debate that humans are not monogamous. This has been researched ad nauseum, although I am too lazy at the moment to dig up the research at the moment.