@deadsuperhero@Lillian I'm with Sean there. I would say that the fat that it affects others or not would be key on my reaction. Also important is to discover if the other person would be willing to reconsider their position. So, to summarize:
Would this affect others? If not, may be it's better not to engage.
If Yes to number 1, does it seem like the person making the point wants to engage in comstructing debate? If Yes, I may try to engage in a civil manner. But...
If I see that the point is being made in bad faith, my observation may take the form of a rebuttal.