Whenever someone posts something like that, instead of giving it attention, just ignore it. It`s easier on all of us because we don`t have to worry about another argument occurring. And even if you don`t care about that, it is detrimental to you as well, as it strengthens their position on things (because they feel under attack); you`re never going to be able to change their opinion, and thus it is a waste of time and energy.