As a direct answer to your question, oceanus, the answer is no. That is to say, how people interact with their family is based on their own experiences (good or bad), and so it's not universally true. There are those who would consider family paramount, and there are those who wouldn't spit on family if they were on fire, and so any rule that implies that either view is always right or always wrong will be inaccurate.
As to how to deal with someone who insists that such a rule must be always right or always wrong, that too depends on the person and the relationship so no single answer works in all cases. Whether bean-dipping someone or arguing/discussing is better is to be decided on a case by case basis. You yourself presented to scenarios that IMHO could be handled differently. In the first case, simple avoidance is rational because someone who wants you to stand behind a relative who did something heinous just because they're related to you isn't likely to be willing to have a rational discussion about it. On the other hand, having lunch with a relative who responds to your comment with something that could trigger discussion might be a place where you'd want to continue (although you weren't rude to bean-dip her like you did if you didn't want to continue).