The only right answer

Discrimination and racism is all part of freedom of speech. You can't have freedom of speech without someone else having the same freedom, and as I once read: freedom of speech is especially necessary for controversial subjects! You don't need freedom of speech to say bunnies are fluffy.
So if someone wants to discriminate: let them! Use ignore if you want, discuss with them, try to change their mind (as if that's ever worked on the internet) or just move on with your day. Who cares what an anonymous person on the internet says? See my personal text to see how much I care.